diff --git a/src/jsifier.mjs b/src/jsifier.mjs
index 6a05135ce6e5e..43f8c51a5be4a 100644
--- a/src/jsifier.mjs
+++ b/src/jsifier.mjs
@@ -44,6 +44,7 @@ import {
   timer,
 } from './utility.mjs';
 import {
+  addedLibraryItems,
   extraExports,
   LibraryManager,
   librarySymbols,
@@ -51,8 +52,6 @@ import {
   shouldExportLibrarySymbol,
 } from './modules.mjs';
 
-const addedLibraryItems = {};
-
 // Debug-only mode (`EMCC_CHECK_DEPS=1` in the environment) that performs a full
 // AST parse on JS library items and reports an error if any local binding
 // shadows a library symbol (which could cause false positives in the
@@ -606,7 +605,7 @@ export async function runJSify(outputFile, symbolsOnly) {
   }
 
   for (const key of Object.keys(LibraryManager.library)) {
-    if (!isDecorator(key)) {
+    if (!isDecorator(key) && !LibraryManager.library[key + '__const']) {
       if (INCLUDE_FULL_LIBRARY || EXPORTED_FUNCTIONS.has(mangleCSymbolName(key))) {
         symbolsNeeded.push(key);
       }
@@ -886,7 +885,10 @@ function(${args}) {
         snippet = new Function('...args', stubFunctionBody);
       }
 
-      librarySymbols.push(mangled);
+      const isConst = LibraryManager.library[symbol + '__const'];
+      if (!isConst) {
+        librarySymbols.push(mangled);
+      }
 
       if (!isStub && LibraryManager.library[symbol + '__export']) {
         extraExports.add(mangled);
@@ -957,7 +959,7 @@ function(${args}) {
       // Check for dependencies on `__internal` symbols from user libraries.
       if (isUserSymbol) {
         for (const dep of deps) {
-          if (LibraryManager.library[dep + '__internal']) {
+          if (LibraryManager.library[dep + '__internal'] && !LibraryManager.library[dep + '__user']) {
             warn(`user library symbol '${symbol}' depends on internal symbol '${dep}'`);
           }
         }
@@ -979,6 +981,9 @@ function(${args}) {
       }
       let contentText;
       if (isFunction) {
+        if (isConst) {
+          error(`JS library error: '__const' decorator cannot be used with functions: '${symbol}'`);
+        }
         // Emit the body of a JS library function.
         if ((USE_ASAN || USE_LSAN) && LibraryManager.library[symbol + '__noleakcheck']) {
           contentText = modifyJSFunction(
@@ -1003,6 +1008,9 @@ function(${args}) {
           contentText = contentText.replace(/function(?:\s+([^(]+))?\s*\(/, `function ${mangled}(`);
         }
       } else if (typeof snippet === 'string' && snippet.startsWith(';')) {
+        if (isConst) {
+          error(`JS library error: '__const' decorator cannot be used with ';'-prefixed snippets: '${symbol}'`);
+        }
         // In JS libraries
         //   foo: ';[code here verbatim]'
         //  emits
@@ -1012,6 +1020,9 @@ function(${args}) {
           contentText += ';';
         }
       } else if (typeof snippet === 'undefined') {
+        if (isConst) {
+          error(`JS library error: '__const' decorator cannot be used with undefined symbols: '${symbol}'`);
+        }
         // For JS library functions that are simply aliases of native symbols,
         // we don't need to generate anything here.  Instead these get included
         // and exported alongside native symbols.
@@ -1029,14 +1040,15 @@ function(${args}) {
         if (typeof snippet === 'string' && snippet[0] == '=') {
           snippet = snippet.slice(1);
         }
-        contentText = `var ${mangled} = ${snippet};`;
+        const declType = isConst ? 'const' : 'var';
+        contentText = `${declType} ${mangled} = ${snippet};`;
       }
 
       if (CHECK_DEPS && (STRICT || !isUserSymbol) && !isStub && contentText) {
         checkShadowing(symbol, mangled, contentText);
       }
 
-      if (contentText && MODULARIZE == 'instance' && shouldExportLibrarySymbol(mangled) && !isStub) {
+      if (contentText && MODULARIZE == 'instance' && shouldExportLibrarySymbol(mangled) && !isStub && !isConst) {
         // In MODULARIZE=instance mode mark JS library symbols are exported at
         // the point of declaration.
         contentText = 'export ' + contentText;
diff --git a/src/lib/libcore.js b/src/lib/libcore.js
index 36958b4c6322f..4d5ed34eded36 100644
--- a/src/lib/libcore.js
+++ b/src/lib/libcore.js
@@ -1478,13 +1478,14 @@ addToLibrary({
 
   // Represents whether emscripten_get_now is guaranteed monotonic; the Date.now
   // implementation is not :(
-  $nowIsMonotonic__internal: true,
+  ...defineInternalConsts({
 #if AUDIO_WORKLET // // https://github.com/WebAudio/web-audio-api/issues/2413
-  $nowIsMonotonic: `!!globalThis.performance?.now;`,
+    $nowIsMonotonic: `!!globalThis.performance?.now;`,
 #else
-  // Modern environment where performance.now() is supported
-  $nowIsMonotonic: 1,
+    // Modern environment where performance.now() is supported
+    $nowIsMonotonic: 1,
 #endif
+  }),
 
   _emscripten_get_now_is_monotonic__internal: true,
   _emscripten_get_now_is_monotonic: () => nowIsMonotonic,
@@ -2410,15 +2411,17 @@ addToLibrary({
   // We used to define these globals unconditionally in support code.
   // Instead, we now define them here so folks can pull it in explicitly, on
   // demand.
-  $STACK_SIZE: {{{ STACK_SIZE }}},
-  $STACK_ALIGN: {{{ STACK_ALIGN }}},
-  $POINTER_SIZE: {{{ POINTER_SIZE }}},
-  $ASSERTIONS: {{{ ASSERTIONS }}},
+  ...defineConsts({
+    $STACK_SIZE: {{{ STACK_SIZE }}},
+    $STACK_ALIGN: {{{ STACK_ALIGN }}},
+    $POINTER_SIZE: {{{ POINTER_SIZE }}},
+    $ASSERTIONS: {{{ ASSERTIONS }}},
+  }),
 });
 
 function autoAddDeps(lib, name) {
   for (const item of Object.keys(lib)) {
-    if (!isDecorator(item)) {
+    if (!isDecorator(item) && item != name && !lib[item + '__const']) {
       lib[item + '__deps'] ??= [];
       lib[item + '__deps'].push(name);
     }
diff --git a/src/lib/libdylink.js b/src/lib/libdylink.js
index ca593f7d4337f..2920bf3c931cd 100644
--- a/src/lib/libdylink.js
+++ b/src/lib/libdylink.js
@@ -10,11 +10,10 @@
 #error "library_dylink.js requires MAIN_MODULE"
 #endif
 
-{{{
-const UNDEFINED_ADDR = to64(-1);
-}}}
-
 var LibraryDylink = {
+  ...defineInternalConsts({
+    $UNDEFINED_ADDR: to64(-1),
+  }),
 #if FILESYSTEM
   $registerWasmPlugin: () => {
     // Use string keys here for public methods to avoid minification since the
@@ -157,7 +156,7 @@ var LibraryDylink = {
 #if DYLINK_DEBUG == 2
         dbg(`new GOT entry: ${symName}`);
 #endif
-        rtn = GOT[symName] = new WebAssembly.Global({'value': '{{{ POINTER_WASM_TYPE }}}', 'mutable': true}, {{{ UNDEFINED_ADDR }}});
+        rtn = GOT[symName] = new WebAssembly.Global({'value': '{{{ POINTER_WASM_TYPE }}}', 'mutable': true}, UNDEFINED_ADDR);
       }
       if (!weakImports.has(symName)) {
         // Any non-weak reference to a symbol marks it as `required`, which
@@ -219,7 +218,7 @@ var LibraryDylink = {
       }
 #endif
 
-      var existingEntry = GOT[symName] && GOT[symName].value != {{{ UNDEFINED_ADDR }}};
+      var existingEntry = GOT[symName] && GOT[symName].value != UNDEFINED_ADDR;
       if (replace || !existingEntry) {
 #if DYLINK_DEBUG == 2
         dbg(`updateGOT: before: ${symName} : ${GOT[symName]?.value}`);
@@ -303,7 +302,7 @@ var LibraryDylink = {
     dbg('reportUndefinedSymbols');
 #endif
     for (var [symName, entry] of Object.entries(GOT)) {
-      if (entry.value == {{{ UNDEFINED_ADDR }}}) {
+      if (entry.value == UNDEFINED_ADDR) {
 #if DYLINK_DEBUG
         dbg(`undef GOT entry: ${symName}`);
 #endif
diff --git a/src/lib/libegl.js b/src/lib/libegl.js
index d44692f1b49c2..a17d0f7d03939 100644
--- a/src/lib/libegl.js
+++ b/src/lib/libegl.js
@@ -15,16 +15,16 @@
  * value of 62006. (multiple creations silently return the same surface)
  */
 
-{{{
-// Magic ID for Emscripten 'default display' 
-const eglDefaultDisplay = 62000;
-// Magic ID for the only EGLConfig supported by Emscripten
-const eglDefaultConfig = 62002;
-// Magic ID for Emscripten EGLContext
-const eglDefaultContext = 62004;
-}}}
-
 var LibraryEGL = {
+  ...defineInternalConsts({
+    // Magic ID for Emscripten 'default display'
+    $eglDefaultDisplay: 62000,
+    // Magic ID for the only EGLConfig supported by Emscripten
+    $eglDefaultConfig: 62002,
+    // Magic ID for Emscripten EGLContext
+    $eglDefaultContext: 62004,
+  }),
+
   $EGL__deps: ['$Browser'],
   $EGL: {
     // This variable tracks the success status of the most recently invoked EGL function call.
@@ -48,7 +48,7 @@ var LibraryEGL = {
     },
 
     chooseConfig(display, attribList, config, config_size, numConfigs) {
-      if (display != {{{ eglDefaultDisplay }}}) {
+      if (display != eglDefaultDisplay) {
         EGL.setErrorCode(0x3008 /* EGL_BAD_DISPLAY */);
         return 0;
       }
@@ -90,7 +90,7 @@ var LibraryEGL = {
         {{{ makeSetValue('numConfigs', '0', '1', 'i32') }}}; // Total number of supported configs: 1.
       }
       if (config && config_size > 0) {
-        {{{ makeSetValue('config', '0', eglDefaultConfig /* Magic ID for the only EGLConfig supported by Emscripten */, '*') }}};
+        {{{ makeSetValue('config', '0', 'eglDefaultConfig' /* Magic ID for the only EGLConfig supported by Emscripten */, '*') }}};
       }
 
       EGL.setErrorCode(0x3000 /* EGL_SUCCESS */);
@@ -108,13 +108,13 @@ var LibraryEGL = {
     if (nativeDisplayType != 0 /* EGL_DEFAULT_DISPLAY */ && nativeDisplayType != 1 /* see library_xlib.js */) {
       return 0; // EGL_NO_DISPLAY
     }
-    return {{{ eglDefaultDisplay }}};
+    return eglDefaultDisplay;
   },
 
   // EGLAPI EGLBoolean EGLAPIENTRY eglInitialize(EGLDisplay dpy, EGLint *major, EGLint *minor);
   eglInitialize__proxy: 'sync',
   eglInitialize: (display, majorVersion, minorVersion) => {
-    if (display != {{{ eglDefaultDisplay }}}) {
+    if (display != eglDefaultDisplay) {
       EGL.setErrorCode(0x3008 /* EGL_BAD_DISPLAY */);
       return 0;
     }
@@ -132,7 +132,7 @@ var LibraryEGL = {
   // EGLAPI EGLBoolean EGLAPIENTRY eglTerminate(EGLDisplay dpy);
   eglTerminate__proxy: 'sync',
   eglTerminate: (display) => {
-    if (display != {{{ eglDefaultDisplay }}}) {
+    if (display != eglDefaultDisplay) {
       EGL.setErrorCode(0x3008 /* EGL_BAD_DISPLAY */);
       return 0;
     }
@@ -157,11 +157,11 @@ var LibraryEGL = {
   // EGLAPI EGLBoolean EGLAPIENTRY eglGetConfigAttrib(EGLDisplay dpy, EGLConfig config, EGLint attribute, EGLint *value);
   eglGetConfigAttrib__proxy: 'sync',
   eglGetConfigAttrib: (display, config, attribute, value) => {
-    if (display != {{{ eglDefaultDisplay }}}) {
+    if (display != eglDefaultDisplay) {
       EGL.setErrorCode(0x3008 /* EGL_BAD_DISPLAY */);
       return 0;
     }
-    if (config != {{{ eglDefaultConfig }}}) {
+    if (config != eglDefaultConfig) {
       EGL.setErrorCode(0x3005 /* EGL_BAD_CONFIG */);
       return 0;
     }
@@ -197,7 +197,7 @@ var LibraryEGL = {
       {{{ makeSetValue('value', '0', '0x3038' /* EGL_NONE */, 'i32') }}};
       return 1;
     case 0x3028: // EGL_CONFIG_ID
-      {{{ makeSetValue('value', '0', eglDefaultConfig, 'i32') }}};
+      {{{ makeSetValue('value', '0', 'eglDefaultConfig', 'i32') }}};
       return 1;
     case 0x3029: // EGL_LEVEL
       {{{ makeSetValue('value', '0', '0' /* Z order/depth layer for this level. Not applicable for Emscripten. */, 'i32') }}};
@@ -274,11 +274,11 @@ var LibraryEGL = {
   // EGLAPI EGLSurface EGLAPIENTRY eglCreateWindowSurface(EGLDisplay dpy, EGLConfig config, EGLNativeWindowType win, const EGLint *attrib_list);
   eglCreateWindowSurface__proxy: 'sync',
   eglCreateWindowSurface: (display, config, win, attrib_list) => {
-    if (display != {{{ eglDefaultDisplay }}}) {
+    if (display != eglDefaultDisplay) {
       EGL.setErrorCode(0x3008 /* EGL_BAD_DISPLAY */);
       return 0;
     }
-    if (config != {{{ eglDefaultConfig }}}) {
+    if (config != eglDefaultConfig) {
       EGL.setErrorCode(0x3005 /* EGL_BAD_CONFIG */);
       return 0;
     }
@@ -293,7 +293,7 @@ var LibraryEGL = {
   // EGLAPI EGLBoolean EGLAPIENTRY eglDestroySurface(EGLDisplay display, EGLSurface surface);
   eglDestroySurface__proxy: 'sync',
   eglDestroySurface: (display, surface) => {
-    if (display != {{{ eglDefaultDisplay }}}) {
+    if (display != eglDefaultDisplay) {
       EGL.setErrorCode(0x3008 /* EGL_BAD_DISPLAY */);
       return 0;
     }
@@ -315,7 +315,7 @@ var LibraryEGL = {
   // EGLAPI EGLContext EGLAPIENTRY eglCreateContext(EGLDisplay dpy, EGLConfig config, EGLContext share_context, const EGLint *attrib_list);
   eglCreateContext__proxy: 'sync',
   eglCreateContext: (display, config, hmm, contextAttribs) => {
-    if (display != {{{ eglDefaultDisplay }}}) {
+    if (display != eglDefaultDisplay) {
       EGL.setErrorCode(0x3008 /* EGL_BAD_DISPLAY */);
       return 0;
     }
@@ -367,7 +367,7 @@ var LibraryEGL = {
 
       // Note: This function only creates a context, but it shall not make it active.
       GL.makeContextCurrent(null);
-      return {{{ eglDefaultContext }}};
+      return eglDefaultContext;
     } else {
       EGL.setErrorCode(0x3009 /* EGL_BAD_MATCH */); // By the EGL 1.4 spec, an implementation that does not support GLES2 (WebGL in this case), this error code is set.
       return 0; /* EGL_NO_CONTEXT */
@@ -378,11 +378,11 @@ var LibraryEGL = {
   // EGLAPI EGLBoolean EGLAPIENTRY eglDestroyContext(EGLDisplay dpy, EGLContext context);
   eglDestroyContext__proxy: 'sync',
   eglDestroyContext: (display, context) => {
-    if (display != {{{ eglDefaultDisplay }}}) {
+    if (display != eglDefaultDisplay) {
       EGL.setErrorCode(0x3008 /* EGL_BAD_DISPLAY */);
       return 0;
     }
-    if (context != {{{ eglDefaultContext }}}) {
+    if (context != eglDefaultContext) {
       EGL.setErrorCode(0x3006 /* EGL_BAD_CONTEXT */);
       return 0;
     }
@@ -398,7 +398,7 @@ var LibraryEGL = {
   // EGLAPI EGLBoolean EGLAPIENTRY eglQuerySurface(EGLDisplay dpy, EGLSurface surface, EGLint attribute, EGLint *value);
   eglQuerySurface__proxy: 'sync',
   eglQuerySurface: (display, surface, attribute, value) => {
-    if (display != {{{ eglDefaultDisplay }}}) {
+    if (display != eglDefaultDisplay) {
       EGL.setErrorCode(0x3008 /* EGL_BAD_DISPLAY */);
       return 0;
     }
@@ -413,7 +413,7 @@ var LibraryEGL = {
     EGL.setErrorCode(0x3000 /* EGL_SUCCESS */);
     switch (attribute) {
     case 0x3028: // EGL_CONFIG_ID
-      {{{ makeSetValue('value', '0', eglDefaultConfig, 'i32') }}};
+      {{{ makeSetValue('value', '0', 'eglDefaultConfig', 'i32') }}};
         return 1;
     case 0x3058: // EGL_LARGEST_PBUFFER
       // Odd EGL API: If surface is not a pbuffer surface, 'value' should not be written to. It's not specified as an error, so true should(?) be returned.
@@ -464,12 +464,12 @@ var LibraryEGL = {
   // EGLAPI EGLBoolean EGLAPIENTRY eglQueryContext(EGLDisplay dpy, EGLContext ctx, EGLint attribute, EGLint *value);
   eglQueryContext__proxy: 'sync',
   eglQueryContext: (display, context, attribute, value) => {
-    if (display != {{{ eglDefaultDisplay }}}) {
+    if (display != eglDefaultDisplay) {
       EGL.setErrorCode(0x3008 /* EGL_BAD_DISPLAY */);
       return 0;
     }
     //\todo An EGL_NOT_INITIALIZED error is generated if EGL is not initialized for dpy.
-    if (context != {{{ eglDefaultContext }}}) {
+    if (context != eglDefaultContext) {
       EGL.setErrorCode(0x3006 /* EGL_BAD_CONTEXT */);
       return 0;
     }
@@ -481,7 +481,7 @@ var LibraryEGL = {
     EGL.setErrorCode(0x3000 /* EGL_SUCCESS */);
     switch (attribute) {
       case 0x3028: // EGL_CONFIG_ID
-        {{{ makeSetValue('value', '0', eglDefaultConfig, 'i32') }}};
+        {{{ makeSetValue('value', '0', 'eglDefaultConfig', 'i32') }}};
         return 1;
       case 0x3097: // EGL_CONTEXT_CLIENT_TYPE
         {{{ makeSetValue('value', '0', '0x30A0' /* EGL_OPENGL_ES_API */, 'i32') }}};
@@ -509,7 +509,7 @@ var LibraryEGL = {
   eglQueryString__noleakcheck: true,
   eglQueryString__proxy: 'sync',
   eglQueryString: (display, name) => {
-    if (display != {{{ eglDefaultDisplay }}}) {
+    if (display != eglDefaultDisplay) {
       EGL.setErrorCode(0x3008 /* EGL_BAD_DISPLAY */);
       return 0;
     }
@@ -570,7 +570,7 @@ var LibraryEGL = {
   // EGLAPI EGLBoolean EGLAPIENTRY eglSwapInterval(EGLDisplay dpy, EGLint interval);
   eglSwapInterval__proxy: 'sync',
   eglSwapInterval: (display, interval) => {
-    if (display != {{{ eglDefaultDisplay }}}) {
+    if (display != eglDefaultDisplay) {
       EGL.setErrorCode(0x3008 /* EGL_BAD_DISPLAY */);
       return 0;
     }
@@ -584,12 +584,12 @@ var LibraryEGL = {
   // EGLAPI EGLBoolean EGLAPIENTRY eglMakeCurrent(EGLDisplay dpy, EGLSurface draw, EGLSurface read, EGLContext ctx);
   eglMakeCurrent__proxy: 'sync',
   eglMakeCurrent: (display, draw, read, context) => {
-    if (display != {{{ eglDefaultDisplay }}}) {
+    if (display != eglDefaultDisplay) {
       EGL.setErrorCode(0x3008 /* EGL_BAD_DISPLAY */);
       return 0 /* EGL_FALSE */;
     }
     //\todo An EGL_NOT_INITIALIZED error is generated if EGL is not initialized for dpy.
-    if (context != 0 && context != {{{ eglDefaultContext }}}) {
+    if (context != 0 && context != eglDefaultContext) {
       EGL.setErrorCode(0x3006 /* EGL_BAD_CONTEXT */);
       return 0;
     }
@@ -626,7 +626,7 @@ var LibraryEGL = {
 
   // EGLAPI EGLDisplay EGLAPIENTRY eglGetCurrentDisplay(void);
   eglGetCurrentDisplay__proxy: 'sync',
-  eglGetCurrentDisplay: () => EGL.currentContext ? {{{ eglDefaultDisplay }}} : 0,
+  eglGetCurrentDisplay: () => EGL.currentContext ? eglDefaultDisplay : 0,
 
   // EGLAPI EGLBoolean EGLAPIENTRY eglSwapBuffers(EGLDisplay dpy, EGLSurface surface);
   eglSwapBuffers__proxy: 'sync',
diff --git a/src/lib/libemval.js b/src/lib/libemval.js
index 498da14c3f578..7d76f8d19797d 100644
--- a/src/lib/libemval.js
+++ b/src/lib/libemval.js
@@ -3,12 +3,15 @@
 // University of Illinois/NCSA Open Source License.  Both these licenses can be
 // found in the LICENSE file.
 
-// Number of handles reserved for non-use (0) or common values w/o refcount.
-{{{
-  const EMVAL_RESERVED_HANDLES = 5;
-  const EMVAL_LAST_RESERVED_HANDLE = EMVAL_RESERVED_HANDLES * 2 - 1;
-}}}
+const NUM_RESERVED_HANDLES = 5;
+
 var LibraryEmVal = {
+  // Number of handles reserved for non-use (0) or common values w/o refcount.
+  ...defineInternalConsts({
+    $EMVAL_RESERVED_HANDLES: NUM_RESERVED_HANDLES,
+    $EMVAL_LAST_RESERVED_HANDLE: NUM_RESERVED_HANDLES * 2 - 1
+  }),
+
   // Stack of handles available for reuse.
   $emval_freelist: [],
 #if !DISABLE_EXCEPTION_CATCHING || WASM_EXCEPTIONS
@@ -24,12 +27,12 @@ var LibraryEmVal = {
     false, 1,
   ],
 #if ASSERTIONS
-  $emval_handles__postset: 'assert(emval_handles.length === {{{ EMVAL_RESERVED_HANDLES }}} * 2)',
+  $emval_handles__postset: 'assert(emval_handles.length === EMVAL_RESERVED_HANDLES * 2)',
 #endif
   $emval_symbols: {}, // address -> string
 
   $count_emval_handles: () => {
-    return emval_handles.length / 2 - {{{ EMVAL_RESERVED_HANDLES }}} - emval_freelist.length;
+    return emval_handles.length / 2 - EMVAL_RESERVED_HANDLES - emval_freelist.length;
   },
 
   _emval_register_symbol: (address) => {
@@ -73,13 +76,13 @@ var LibraryEmVal = {
   },
 
   _emval_incref: (handle) => {
-    if (handle > {{{ EMVAL_LAST_RESERVED_HANDLE }}}) {
+    if (handle > EMVAL_LAST_RESERVED_HANDLE) {
       emval_handles[handle + 1] += 1;
     }
   },
 
   _emval_decref: (handle) => {
-    if (handle > {{{ EMVAL_LAST_RESERVED_HANDLE }}} && 0 === --emval_handles[handle + 1]) {
+    if (handle > EMVAL_LAST_RESERVED_HANDLE && 0 === --emval_handles[handle + 1]) {
   #if ASSERTIONS
       assert(emval_handles[handle] !== undefined, `decref for unallocated handle`);
   #endif
diff --git a/src/lib/libint53.js b/src/lib/libint53.js
index ee06b3eab08de..c8c425fcb6b23 100644
--- a/src/lib/libint53.js
+++ b/src/lib/libint53.js
@@ -119,8 +119,10 @@ addToLibrary({
   },
 
 #if WASM_BIGINT
-  $INT53_MAX: '{{{ Math.pow(2, 53) }}}',
-  $INT53_MIN: '-{{{ Math.pow(2, 53) }}}',
+  ...defineConsts({
+    $INT53_MAX: 2 ** 53,
+    $INT53_MIN: -(2 ** 53),
+  }),
   // Convert a bigint value (usually coming from Wasm->JS call) into an int53
   // JS Number.  This is used when we have an incoming i64 that we know is a
   // pointer or size_t and is expected to be within the int53 range.
diff --git a/src/lib/libpthread.js b/src/lib/libpthread.js
index eabb60ac34f87..fdfcb81ce1b29 100644
--- a/src/lib/libpthread.js
+++ b/src/lib/libpthread.js
@@ -24,23 +24,6 @@
 #endif
 
 {{{
-#if MEMORY64
-const MAX_PTR = Number((2n ** 64n) - 1n);
-#else
-const MAX_PTR = (2 ** 32) - 1
-#endif
-
-// Message IDs used when communicating with workers via postMessage.
-const CMD_LOAD = 1;
-const CMD_RUN = 2;
-const CMD_LOADED = 3;
-const CMD_CHECK_MAILBOX = 4;
-const CMD_SPAWN_THREAD = 5;
-const CMD_CLEANUP_THREAD = 6;
-const CMD_MARK_AS_FINISHED = 7;
-const CMD_UNCAUGHT_EXN = 8;
-const CMD_CALL_HANDLER = 9;
-
 #if WASM_ESM_INTEGRATION
 const pthreadWorkerScript = TARGET_BASENAME + '.pthread.mjs';
 #else
@@ -79,6 +62,22 @@ const pthreadWorkerOptions = `{
 }}}
 
 var LibraryPThread = {
+  // Message IDs used when communicating with workers via postMessage.
+  ...defineInternalConsts({
+    $CMD_LOAD: 1,
+    $CMD_RUN: 2,
+    $CMD_LOADED: 3,
+    $CMD_CHECK_MAILBOX: 4,
+    $CMD_SPAWN_THREAD: 5,
+    $CMD_CLEANUP_THREAD: 6,
+    $CMD_MARK_AS_FINISHED: 7,
+    $CMD_UNCAUGHT_EXN: 8,
+    $CMD_CALL_HANDLER: 9,
+#if OFFSCREENCANVASES_TO_PTHREAD
+    $MAX_PTR: MEMORY64 ? Number((2n ** 64n) - 1n) : (2 ** 32) - 1,
+#endif
+  }),
+
   $PThread__postset: 'PThread.init();',
   $PThread__deps: [
     '_emscripten_thread_init',
@@ -298,24 +297,24 @@ var LibraryPThread = {
         }
 
         switch (cmd) {
-          case {{{ CMD_CHECK_MAILBOX }}}:
+          case CMD_CHECK_MAILBOX:
             checkMailbox();
             break;
-          case {{{ CMD_SPAWN_THREAD }}}:
+          case CMD_SPAWN_THREAD:
             spawnThread(d);
             break;
-          case {{{ CMD_CLEANUP_THREAD }}}:
+          case CMD_CLEANUP_THREAD:
             // cleanupThread needs to be run via callUserCallback since it calls
             // back into user code to free thread data. Without this it's possible
             // the unwind or ExitStatus exception could escape here.
             callUserCallback(() => cleanupThread(d.thread));
             break;
 #if MAIN_MODULE
-          case {{{ CMD_MARK_AS_FINISHED }}}:
+          case CMD_MARK_AS_FINISHED:
             markAsFinished(d.thread);
             break;
 #endif
-          case {{{ CMD_LOADED }}}:
+          case CMD_LOADED:
 #if ENVIRONMENT_MAY_BE_NODE
             if (ENVIRONMENT_IS_NODE && !worker.strongref) {
               // Once worker is loaded & idle, mark it as weakly referenced,
@@ -327,14 +326,14 @@ var LibraryPThread = {
             onFinishedLoading(worker);
             break;
 #if ENVIRONMENT_MAY_BE_NODE
-          case {{{ CMD_UNCAUGHT_EXN }}}:
+          case CMD_UNCAUGHT_EXN:
             // Message handler for Node.js specific out-of-order behavior:
             // https://github.com/nodejs/node/issues/59617
             // A pthread sent an uncaught exception event. Re-raise it on the main thread.
             worker.onerror(d.error);
             break;
 #endif
-          case {{{ CMD_CALL_HANDLER }}}:
+          case CMD_CALL_HANDLER:
             Module[d.handler](...d.args);
             break;
           default:
@@ -414,7 +413,7 @@ var LibraryPThread = {
 
       // Ask the new worker to load up the Emscripten-compiled page. This is a heavy operation.
       worker.postMessage({
-        cmd: {{{ CMD_LOAD }}},
+        cmd: CMD_LOAD,
         handlers: handlers,
 #if WASM2JS
         // the polyfill WebAssembly.Memory instance has function properties,
@@ -611,7 +610,7 @@ var LibraryPThread = {
     dbg(`_emscripten_thread_cleanup: ${ptrToString(thread)}`)
 #endif
     if (!ENVIRONMENT_IS_PTHREAD) cleanupThread(thread);
-    else postMessage({ cmd: {{{ CMD_CLEANUP_THREAD }}}, thread });
+    else postMessage({ cmd: CMD_CLEANUP_THREAD, thread });
   },
 
   _emscripten_thread_set_strongref: (thread) => {
@@ -717,7 +716,7 @@ var LibraryPThread = {
 
     worker.pthread_ptr = threadParams.pthread_ptr;
     var msg = {
-        cmd: {{{ CMD_RUN }}},
+        cmd: CMD_RUN,
         start_routine: threadParams.startRoutine,
         arg: threadParams.arg,
         pthread_ptr: threadParams.pthread_ptr,
@@ -803,7 +802,7 @@ var LibraryPThread = {
     // Proxied canvases string pointer -1/MAX_PTR is used as a special token to
     // fetch whatever canvases were passed to build in
     // -sOFFSCREENCANVASES_TO_PTHREAD= command line.
-    if (transferredCanvasNames == {{{ MAX_PTR }}}) {
+    if (transferredCanvasNames == MAX_PTR) {
       transferredCanvasNames = '{{{ OFFSCREENCANVASES_TO_PTHREAD }}}';
     } else
 #endif
@@ -930,7 +929,7 @@ var LibraryPThread = {
       // The prepopulated pool of web workers that can host pthreads is stored
       // in the main JS thread. Therefore if a pthread is attempting to spawn a
       // new thread, the thread creation must be deferred to the main JS thread.
-      threadParams.cmd = {{{ CMD_SPAWN_THREAD }}};
+      threadParams.cmd = CMD_SPAWN_THREAD;
       postMessage(threadParams, transferList);
       // When we defer thread creation this way, we have no way to detect thread
       // creation synchronously today, so we have to assume success and return 0.
@@ -1195,7 +1194,7 @@ var LibraryPThread = {
     // running, but remain around waiting to be joined.  In this state they
     // cannot run any more proxied work.
     if (!ENVIRONMENT_IS_PTHREAD) markAsFinished(thread);
-    else postMessage({ cmd: {{{ CMD_MARK_AS_FINISHED }}}, thread });
+    else postMessage({ cmd: CMD_MARK_AS_FINISHED, thread });
   },
 
   _emscripten_thread_free_tls: () => PThread.tlsFreeFunctions.forEach((f) => f()),
@@ -1332,7 +1331,7 @@ var LibraryPThread = {
     if (targetThread == currThreadId) {
       setTimeout(checkMailbox);
     } else if (ENVIRONMENT_IS_PTHREAD) {
-      postMessage({targetThread, cmd: {{{ CMD_CHECK_MAILBOX }}}});
+      postMessage({targetThread, cmd: CMD_CHECK_MAILBOX});
     } else {
       var worker = PThread.pthreads[targetThread];
       if (!worker) {
@@ -1341,7 +1340,7 @@ var LibraryPThread = {
 #endif
         return;
       }
-      worker.postMessage({cmd: {{{ CMD_CHECK_MAILBOX }}}});
+      worker.postMessage({cmd: CMD_CHECK_MAILBOX});
     }
   }
 };
diff --git a/src/lib/libsockfs_node.js b/src/lib/libsockfs_node.js
index cc0344dafe0a9..cb55db0ce41e9 100644
--- a/src/lib/libsockfs_node.js
+++ b/src/lib/libsockfs_node.js
@@ -43,18 +43,17 @@
 // shared) wasm memory before being handed to node, so a SharedArrayBuffer heap
 // is safe.
 
-{{{
-// sock.state lifecycle, substituted as numbers at build time. A fresh socket
-// has an undefined (falsy) state until its first bind/connect.
-const SOCK_STATE_CONNECTING = 1;
-const SOCK_STATE_CONNECTED = 2;
-const SOCK_STATE_BOUND = 3;
-const SOCK_STATE_LISTEN = 4;
-const SOCK_STATE_CLOSED = 5;
-null;
-}}}
-
 var NodeSockFSLibrary = {
+  // sock.state lifecycle. A fresh socket has an undefined (falsy) state until
+  // its first bind/connect.
+  ...defineInternalConsts({
+    $SOCK_STATE_CONNECTING: 1,
+    $SOCK_STATE_CONNECTED: 2,
+    $SOCK_STATE_BOUND: 3,
+    $SOCK_STATE_LISTEN: 4,
+    $SOCK_STATE_CLOSED: 5,
+  }),
+
   // Node plumbing shared by the interface methods below.
   $nodeSockHelpers: {
     // node builtins, resolved once each. getBuiltinModule works in both
@@ -434,7 +433,7 @@ var NodeSockFSLibrary = {
       });
       conn.on('close', () => {
         sock.readClosed = true;
-        sock.state = {{{ SOCK_STATE_CLOSED }}};
+        sock.state = SOCK_STATE_CLOSED;
         SOCKFS.emit('close', sock.stream.fd);
       });
       // Backpressure relieved, so we are writable again.
@@ -445,7 +444,7 @@ var NodeSockFSLibrary = {
       conn.on('error', (e) => {
         sock.error = nodeSockHelpers.nodeErrToErrno(e);
         // Let a failed connect resolve so SO_ERROR can be read.
-        if (sock.state === {{{ SOCK_STATE_CONNECTING }}}) sock.state = {{{ SOCK_STATE_CONNECTED }}};
+        if (sock.state === SOCK_STATE_CONNECTING) sock.state = SOCK_STATE_CONNECTED;
         SOCKFS.emit('error', [sock.stream.fd, sock.error, (e && e.message) || 'socket error']);
       });
     },
@@ -475,7 +474,7 @@ var NodeSockFSLibrary = {
         // POLLERR|POLLHUP, plus writable so SO_ERROR can be read. POLLOUT|POLLERR
         // also satisfies epoll's is_write_closed() mapping.
         mask |= {{{ cDefs.POLLOUT }}} | {{{ cDefs.POLLERR }}} | {{{ cDefs.POLLHUP }}};
-      } else if (sock.connection && sock.state === {{{ SOCK_STATE_CONNECTED }}} && !sock.writeBlocked) {
+      } else if (sock.connection && sock.state === SOCK_STATE_CONNECTED && !sock.writeBlocked) {
         mask |= {{{ cDefs.POLLOUT }}};
       }
       // A peer FIN / read-side hangup (recv will see EOF) is POLLRDHUP. POLLHUP
@@ -483,7 +482,7 @@ var NodeSockFSLibrary = {
       // we locally shut down both directions (shutdown(SHUT_RDWR)), which Linux
       // epoll reports as a hangup even though the node connection is still live.
       if (sock.readClosed) mask |= {{{ cDefs.POLLRDHUP }}};
-      if (sock.state === {{{ SOCK_STATE_CLOSED }}} || (sock.readClosed && sock.writeShutdown)) {
+      if (sock.state === SOCK_STATE_CLOSED || (sock.readClosed && sock.writeShutdown)) {
         mask |= {{{ cDefs.POLLHUP }}};
       }
       return mask;
@@ -504,7 +503,7 @@ var NodeSockFSLibrary = {
       }
     },
     close(sock) {
-      sock.state = {{{ SOCK_STATE_CLOSED }}};
+      sock.state = SOCK_STATE_CLOSED;
       if (sock.udp) {
         try {
           if (sock.udpPublic) sock.udp.close();
@@ -562,7 +561,7 @@ var NodeSockFSLibrary = {
         // addr is a filesystem path (or an abstract '\0...' name). Bind
         // synchronously so EADDRINUSE surfaces here and getsockname() works.
         nodeSockHelpers.bindPipe(sock, addr);
-        sock.state = {{{ SOCK_STATE_BOUND }}};
+        sock.state = SOCK_STATE_BOUND;
         return;
       }
       if (sock.type === {{{ cDefs.SOCK_DGRAM }}}) {
@@ -589,7 +588,7 @@ var NodeSockFSLibrary = {
           sock.saddr = uname.address;
           sock.sport = uname.port;
         }
-        sock.state = {{{ SOCK_STATE_BOUND }}};
+        sock.state = SOCK_STATE_BOUND;
         nodeSockHelpers.startUdpRecv(sock);
         return;
       }
@@ -597,21 +596,21 @@ var NodeSockFSLibrary = {
       // a bind(:0)) is known immediately, getsockname() needs no promotion, and a
       // conflict surfaces right here as EADDRINUSE.
       nodeSockHelpers.bindHandle(sock, addr, port);
-      sock.state = {{{ SOCK_STATE_BOUND }}};
+      sock.state = SOCK_STATE_BOUND;
     },
     connect(sock, addr, port) {
       if (sock.family === {{{ cDefs.AF_UNIX }}}) {
         if (sock.server) throw new FS.ErrnoError({{{ cDefs.EOPNOTSUPP }}});
         if (sock.connection) {
-          throw new FS.ErrnoError(sock.state === {{{ SOCK_STATE_CONNECTING }}} ? {{{ cDefs.EALREADY }}} : {{{ cDefs.EISCONN }}});
+          throw new FS.ErrnoError(sock.state === SOCK_STATE_CONNECTING ? {{{ cDefs.EALREADY }}} : {{{ cDefs.EISCONN }}});
         }
         // addr is the peer path. node reports no name back, so record it as the
         // peer name ourselves; the local end is unnamed unless bind() named it.
         sock.daddr = addr;
-        sock.state = {{{ SOCK_STATE_CONNECTING }}};
+        sock.state = SOCK_STATE_CONNECTING;
         var uconn = new (nodeSockHelpers.getNet().Socket)({ allowHalfOpen: true });
         uconn.once('connect', () => {
-          sock.state = {{{ SOCK_STATE_CONNECTED }}};
+          sock.state = SOCK_STATE_CONNECTED;
           sock.saddr ??= '';
           try { uconn.resume(); } catch (e) {}
           SOCKFS.emit('open', sock.stream.fd);
@@ -651,11 +650,11 @@ var NodeSockFSLibrary = {
       }
       if (sock.server) throw new FS.ErrnoError({{{ cDefs.EOPNOTSUPP }}});
       if (sock.connection) {
-        throw new FS.ErrnoError(sock.state === {{{ SOCK_STATE_CONNECTING }}} ? {{{ cDefs.EALREADY }}} : {{{ cDefs.EISCONN }}});
+        throw new FS.ErrnoError(sock.state === SOCK_STATE_CONNECTING ? {{{ cDefs.EALREADY }}} : {{{ cDefs.EISCONN }}});
       }
       sock.daddr = addr;
       sock.dport = port;
-      sock.state = {{{ SOCK_STATE_CONNECTING }}};
+      sock.state = SOCK_STATE_CONNECTING;
       var net = nodeSockHelpers.getNet();
       if (!sock.bound) {
         // The kernel assigns the ephemeral source port synchronously at
@@ -668,7 +667,7 @@ var NodeSockFSLibrary = {
       // honored by the kernel.
       var conn = new net.Socket({ handle: sock.bound, pauseOnCreate: true, allowHalfOpen: true });
       conn.once('connect', () => {
-        sock.state = {{{ SOCK_STATE_CONNECTED }}};
+        sock.state = SOCK_STATE_CONNECTED;
         sock.saddr = conn.localAddress;
         sock.sport = conn.localPort;
         sock.daddr = conn.remoteAddress || addr;
@@ -698,14 +697,14 @@ var NodeSockFSLibrary = {
         // bind is eager and synchronous (bindHandle), so the assigned port is
         // known and any conflict surfaces before we listen.
         nodeSockHelpers.bindHandle(sock, '0.0.0.0', 0);
-        sock.state = {{{ SOCK_STATE_BOUND }}};
+        sock.state = SOCK_STATE_BOUND;
       }
       var server = new (nodeSockHelpers.getNet().Server)({ pauseOnConnect: true, allowHalfOpen: true });
       sock.server = server;
-      sock.state = {{{ SOCK_STATE_LISTEN }}};
+      sock.state = SOCK_STATE_LISTEN;
       server.on('connection', (conn) => {
         var newsock = SOCKFS.createSocket(sock.family, sock.type, sock.protocol);
-        newsock.state = {{{ SOCK_STATE_CONNECTED }}};
+        newsock.state = SOCK_STATE_CONNECTED;
         if (isUnix) {
           // node reports no name for a pipe: the accepted socket's local name is
           // the listener's path, the peer is unnamed (the client rarely binds).
@@ -785,7 +784,7 @@ var NodeSockFSLibrary = {
         throw new FS.ErrnoError({{{ cDefs.EPIPE }}});
       }
       var conn = sock.connection;
-      if (!conn || sock.state === {{{ SOCK_STATE_CLOSED }}}) {
+      if (!conn || sock.state === SOCK_STATE_CLOSED) {
         throw new FS.ErrnoError({{{ cDefs.ENOTCONN }}});
       }
       // Bound node's write buffer to its high-water mark: a non-blocking socket
@@ -1019,7 +1018,7 @@ var NodeSockFSLibrary = {
           // TCP_MAXSEG: node exposes no MSS, so report RFC 879's 536-byte default
           // before the handshake and the (large) loopback-negotiated value once
           // connected. Enough for callers that only compare pre/post-connect MSS.
-          case 2: val = (sock.state === {{{ SOCK_STATE_CONNECTED }}}) ? 65483 : 536; break;
+          case 2: val = (sock.state === SOCK_STATE_CONNECTED) ? 65483 : 536; break;
           case 1: val = sock.opts.noDelay ? 1 : 0; break;    // TCP_NODELAY
           case 4: val = sock.opts.keepAliveIdle || 0; break; // TCP_KEEPIDLE
           case 5: val = sock.opts.keepAliveIntvl || 0; break;// TCP_KEEPINTVL
diff --git a/src/lib/libwasm_worker.js b/src/lib/libwasm_worker.js
index 778638905d059..3e1884122a848 100644
--- a/src/lib/libwasm_worker.js
+++ b/src/lib/libwasm_worker.js
@@ -22,10 +22,6 @@
 #endif // ~WASM_WORKERS
 
 {{{
-#if !PTHREADS
-  // In pthread builds this gets defined in libpthread.js
-  const CMD_UNCAUGHT_EXN = 8;
-#endif
   const workerSupportsFutexWait = () => AUDIO_WORKLET ? '!ENVIRONMENT_IS_AUDIO_WORKLET' : '1';
   const wasmWorkerJs = `
 #if MINIMAL_RUNTIME
@@ -62,6 +58,12 @@
 
 
 addToLibrary({
+#if !PTHREADS
+  ...defineInternalConsts({
+    $CMD_UNCAUGHT_EXN: 8,
+  }),
+#endif
+
   $_wasmWorkers: {},
 #if TRUSTED_TYPES
   // Cached Trusted Types policy for Wasm Worker creation.
@@ -210,7 +212,7 @@ if (ENVIRONMENT_IS_WASM_WORKER
     if (ENVIRONMENT_IS_NODE) {
       /** @suppress {checkTypes} */
       worker.on('message', (msg) => {
-        if (msg.cmd == {{{ CMD_UNCAUGHT_EXN }}}) {
+        if (msg.cmd == CMD_UNCAUGHT_EXN) {
           // Message handler for Node.js specific out-of-order behavior:
           // https://github.com/nodejs/node/issues/59617
           // A worker sent an uncaught exception event. Re-raise it on the main thread.
diff --git a/src/lib/libwebgl.js b/src/lib/libwebgl.js
index d90d3b2a9ba18..03e485973de83 100644
--- a/src/lib/libwebgl.js
+++ b/src/lib/libwebgl.js
@@ -4,11 +4,7 @@
  * SPDX-License-Identifier: MIT
  */
 
-// Specifies the size of the GL temp buffer pool, in bytes. Must be a multiple
-// of 9 and 16.
 {{{
-  const GL_POOL_TEMP_BUFFERS_SIZE = 2*9*16 // = 288
-
   const isCurrentContextWebGL2 = () => {
     // This function should only be called inside of `#if MAX_WEBGL_VERSION >= 2` blocks
     assert(MAX_WEBGL_VERSION >= 2, 'isCurrentContextWebGL2 called without webgl2 support');
@@ -18,6 +14,12 @@
 }}}
 
 var LibraryGL = {
+  // Specifies the size of the GL temp buffer pool, in bytes. Must be a multiple
+  // of 9 and 16.
+  ...defineInternalConsts({
+    $GL_POOL_TEMP_BUFFERS_SIZE: 2 * 9 * 16, // = 288
+  }),
+
   // For functions such as glDrawBuffers, glInvalidateFramebuffer and
   // glInvalidateSubFramebuffer that need to pass a short array to the WebGL
   // API, create a set of short fixed-length arrays to avoid having to generate
@@ -26,16 +28,16 @@ var LibraryGL = {
   $tempFixedLengthArray: [],
 
   $miniTempWebGLFloatBuffers: [],
-  $miniTempWebGLFloatBuffers__postset: `var miniTempWebGLFloatBuffersStorage = new Float32Array({{{ GL_POOL_TEMP_BUFFERS_SIZE }}});
+  $miniTempWebGLFloatBuffers__postset: `var miniTempWebGLFloatBuffersStorage = new Float32Array(GL_POOL_TEMP_BUFFERS_SIZE);
 // Create GL_POOL_TEMP_BUFFERS_SIZE+1 temporary buffers, for uploads of size 0 through GL_POOL_TEMP_BUFFERS_SIZE inclusive
-for (/**@suppress{duplicate}*/var i = 0; i <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}}; ++i) {
+for (/**@suppress{duplicate}*/var i = 0; i <= GL_POOL_TEMP_BUFFERS_SIZE; ++i) {
   miniTempWebGLFloatBuffers[i] = miniTempWebGLFloatBuffersStorage.subarray(0, i);
 }`,
 
   $miniTempWebGLIntBuffers: [],
-  $miniTempWebGLIntBuffers__postset: `var miniTempWebGLIntBuffersStorage = new Int32Array({{{ GL_POOL_TEMP_BUFFERS_SIZE }}});
+  $miniTempWebGLIntBuffers__postset: `var miniTempWebGLIntBuffersStorage = new Int32Array(GL_POOL_TEMP_BUFFERS_SIZE);
 // Create GL_POOL_TEMP_BUFFERS_SIZE+1 temporary buffers, for uploads of size 0 through GL_POOL_TEMP_BUFFERS_SIZE inclusive
-for (/**@suppress{duplicate}*/var i = 0; i <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}}; ++i) {
+for (/**@suppress{duplicate}*/var i = 0; i <= GL_POOL_TEMP_BUFFERS_SIZE; ++i) {
   miniTempWebGLIntBuffers[i] = miniTempWebGLIntBuffersStorage.subarray(0, i);
 }`,
 
@@ -2438,7 +2440,7 @@ for (/**@suppress{duplicate}*/var i = 0; i <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}};
 #endif
 
 #if GL_POOL_TEMP_BUFFERS
-    if (count <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}}) {
+    if (count <= GL_POOL_TEMP_BUFFERS_SIZE) {
       // avoid allocation when uploading few enough uniforms
       var view = miniTempWebGLIntBuffers[count];
       for (var i = 0; i < count; ++i) {
@@ -2474,7 +2476,7 @@ for (/**@suppress{duplicate}*/var i = 0; i <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}};
 #endif
 
 #if GL_POOL_TEMP_BUFFERS
-    if (count <= {{{ GL_POOL_TEMP_BUFFERS_SIZE / 2 }}}) {
+    if (count <= GL_POOL_TEMP_BUFFERS_SIZE / 2) {
       // avoid allocation when uploading few enough uniforms
       count *= 2;
       var view = miniTempWebGLIntBuffers[count];
@@ -2512,7 +2514,7 @@ for (/**@suppress{duplicate}*/var i = 0; i <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}};
 #endif
 
 #if GL_POOL_TEMP_BUFFERS
-    if (count <= {{{ GL_POOL_TEMP_BUFFERS_SIZE / 3 }}}) {
+    if (count <= GL_POOL_TEMP_BUFFERS_SIZE / 3) {
       // avoid allocation when uploading few enough uniforms
       count *= 3;
       var view = miniTempWebGLIntBuffers[count];
@@ -2551,7 +2553,7 @@ for (/**@suppress{duplicate}*/var i = 0; i <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}};
 #endif
 
 #if GL_POOL_TEMP_BUFFERS
-    if (count <= {{{ GL_POOL_TEMP_BUFFERS_SIZE / 4 }}}) {
+    if (count <= GL_POOL_TEMP_BUFFERS_SIZE / 4) {
       // avoid allocation when uploading few enough uniforms
       count *= 4;
       var view = miniTempWebGLIntBuffers[count];
@@ -2591,7 +2593,7 @@ for (/**@suppress{duplicate}*/var i = 0; i <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}};
 #endif
 
 #if GL_POOL_TEMP_BUFFERS
-    if (count <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}}) {
+    if (count <= GL_POOL_TEMP_BUFFERS_SIZE) {
       // avoid allocation when uploading few enough uniforms
       var view = miniTempWebGLFloatBuffers[count];
       for (var i = 0; i < count; ++i) {
@@ -2627,7 +2629,7 @@ for (/**@suppress{duplicate}*/var i = 0; i <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}};
 #endif
 
 #if GL_POOL_TEMP_BUFFERS
-    if (count <= {{{ GL_POOL_TEMP_BUFFERS_SIZE / 2 }}}) {
+    if (count <= GL_POOL_TEMP_BUFFERS_SIZE / 2) {
       // avoid allocation when uploading few enough uniforms
       count *= 2;
       var view = miniTempWebGLFloatBuffers[count];
@@ -2665,7 +2667,7 @@ for (/**@suppress{duplicate}*/var i = 0; i <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}};
 #endif
 
 #if GL_POOL_TEMP_BUFFERS
-    if (count <= {{{ GL_POOL_TEMP_BUFFERS_SIZE / 3 }}}) {
+    if (count <= GL_POOL_TEMP_BUFFERS_SIZE / 3) {
       // avoid allocation when uploading few enough uniforms
       count *= 3;
       var view = miniTempWebGLFloatBuffers[count];
@@ -2704,7 +2706,7 @@ for (/**@suppress{duplicate}*/var i = 0; i <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}};
 #endif
 
 #if GL_POOL_TEMP_BUFFERS
-    if (count <= {{{ GL_POOL_TEMP_BUFFERS_SIZE / 4 }}}) {
+    if (count <= GL_POOL_TEMP_BUFFERS_SIZE / 4) {
       // avoid allocation when uploading few enough uniforms
       var view = miniTempWebGLFloatBuffers[4*count];
       // hoist the heap out of the loop for size and for pthreads+growth.
@@ -2748,7 +2750,7 @@ for (/**@suppress{duplicate}*/var i = 0; i <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}};
 #endif
 
 #if GL_POOL_TEMP_BUFFERS
-    if (count <= {{{ GL_POOL_TEMP_BUFFERS_SIZE / 4 }}}) {
+    if (count <= GL_POOL_TEMP_BUFFERS_SIZE / 4) {
       // avoid allocation when uploading few enough uniforms
       count *= 4;
       var view = miniTempWebGLFloatBuffers[count];
@@ -2788,7 +2790,7 @@ for (/**@suppress{duplicate}*/var i = 0; i <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}};
 #endif
 
 #if GL_POOL_TEMP_BUFFERS
-    if (count <= {{{ GL_POOL_TEMP_BUFFERS_SIZE / 9 }}}) {
+    if (count <= GL_POOL_TEMP_BUFFERS_SIZE / 9) {
       // avoid allocation when uploading few enough uniforms
       count *= 9;
       var view = miniTempWebGLFloatBuffers[count];
@@ -2833,7 +2835,7 @@ for (/**@suppress{duplicate}*/var i = 0; i <= {{{ GL_POOL_TEMP_BUFFERS_SIZE }}};
 #endif
 
 #if GL_POOL_TEMP_BUFFERS
-    if (count <= {{{ GL_POOL_TEMP_BUFFERS_SIZE / 16 }}}) {
+    if (count <= GL_POOL_TEMP_BUFFERS_SIZE / 16) {
       // avoid allocation when uploading few enough uniforms
       var view = miniTempWebGLFloatBuffers[16*count];
       // hoist the heap out of the loop for size and for pthreads+growth.
diff --git a/src/modules.mjs b/src/modules.mjs
index 3691e964b69c2..a0ab61dbc9930 100644
--- a/src/modules.mjs
+++ b/src/modules.mjs
@@ -30,6 +30,7 @@ import {preprocess, processMacros} from './parseTools.mjs';
 
 // List of symbols that were added from the library.
 export const librarySymbols = [];
+export const addedLibraryItems = {};
 // Library symbols exported via the `__export` decorator.
 export const extraExports = new Set();
 // Map of library symbols which are aliases for native symbols
@@ -438,14 +439,12 @@ function isInternalSymbol(ident) {
 }
 
 function getUnusedLibrarySymbols() {
-  const librarySymbolSet = new Set(librarySymbols);
   const missingSyms = new Set();
   for (const [ident, value] of Object.entries(LibraryManager.library)) {
     if (typeof value === 'function' || typeof value === 'number') {
       if (isJsOnlySymbol(ident) && !isDecorator(ident) && !isInternalSymbol(ident)) {
-        const name = ident.slice(1);
-        if (!librarySymbolSet.has(name)) {
-          missingSyms.add(name);
+        if (!(ident in addedLibraryItems)) {
+          missingSyms.add(ident.slice(1));
         }
       }
     }
diff --git a/src/runtime_common.js b/src/runtime_common.js
index 0ed87c326ed4c..3c29b7fae0738 100644
--- a/src/runtime_common.js
+++ b/src/runtime_common.js
@@ -55,7 +55,7 @@ if (ENVIRONMENT_IS_NODE && {{{ ENVIRONMENT_IS_WORKER_THREAD() }}}) {
 #if PTHREADS_DEBUG
     dbg(`uncaughtException on worker thread: ${err.message}`);
 #endif
-    postMessage({ cmd: {{{ CMD_UNCAUGHT_EXN }}}, error: err });
+    postMessage({ cmd: CMD_UNCAUGHT_EXN, error: err });
     // Also shut down the Worker to match the same semantics as if this uncaughtException
     // handler was not registered.
     // (n.b. this will not shut down the whole Node.js app process, but just the Worker)
diff --git a/src/runtime_pthread.js b/src/runtime_pthread.js
index 27996fc16499e..b3bb1ba22fbfa 100644
--- a/src/runtime_pthread.js
+++ b/src/runtime_pthread.js
@@ -46,7 +46,7 @@ if (ENVIRONMENT_IS_PTHREAD) {
       var msgData = e.data;
       //dbg('msgData: ' + Object.keys(msgData));
       var cmd = msgData.cmd;
-      if (cmd == {{{ CMD_LOAD }}}) { // Preload command that is called once per worker to parse and load the Emscripten code.
+      if (cmd == CMD_LOAD) { // Preload command that is called once per worker to parse and load the Emscripten code.
 #if ASSERTIONS
         workerID = msgData.workerID;
 #endif
@@ -61,7 +61,7 @@ if (ENVIRONMENT_IS_PTHREAD) {
         // And add a callback for when the runtime is initialized.
         startWorker = () => {
           // Notify the main thread that this thread has loaded.
-          postMessage({ cmd: {{{ CMD_LOADED }}} });
+          postMessage({ cmd: CMD_LOADED });
           // Process any messages that were queued before the thread was ready.
           for (let msg of messageQueue) {
             handleMessage(msg);
@@ -92,7 +92,7 @@ if (ENVIRONMENT_IS_PTHREAD) {
 #if RUNTIME_DEBUG
               dbg(`worker: calling handler on main thread: ${handler}`);
 #endif
-              postMessage({ cmd: {{{ CMD_CALL_HANDLER }}}, handler, args: args });
+              postMessage({ cmd: CMD_CALL_HANDLER, handler, args: args });
             }
             // Rebind the out / err handlers if needed
             if (handler == 'print') out = Module[handler];
@@ -130,7 +130,7 @@ if (ENVIRONMENT_IS_PTHREAD) {
 #if !MINIMAL_RUNTIME
         startWorker();
 #endif
-      } else if (cmd == {{{ CMD_RUN }}}) {
+      } else if (cmd == CMD_RUN) {
 #if ASSERTIONS
         assert(msgData.pthread_ptr);
         assert(wasmMemory, "CMD_RUN received before CMD_LOAD");
@@ -177,7 +177,7 @@ if (ENVIRONMENT_IS_PTHREAD) {
           dbg(`worker: Pthread 0x${_pthread_self().toString(16)} completed its main entry point with an 'unwind', keeping the worker alive for asynchronous operation.`);
 #endif
         }
-      } else if (cmd == {{{ CMD_CHECK_MAILBOX }}}) {
+      } else if (cmd == CMD_CHECK_MAILBOX) {
         if (initializedJS) {
           checkMailbox();
         }
diff --git a/src/utility.mjs b/src/utility.mjs
index c163f82189f79..f3670f7065333 100644
--- a/src/utility.mjs
+++ b/src/utility.mjs
@@ -186,6 +186,7 @@ export function mergeInto(obj, other, options = null) {
           __i53abi: 'boolean',
           __export: 'boolean',
           __force: 'boolean',
+          __const: 'boolean',
         };
         const expected = decoratorTypes[decoratorName];
         if (type !== expected && !expected.includes(type)) {
@@ -223,12 +224,30 @@ export const decoratorSuffixes = [
   '__i53abi',
   '__export',
   '__force',
+  '__const',
 ];
 
 export function isDecorator(ident) {
   return decoratorSuffixes.some((suffix) => ident.endsWith(suffix));
 }
 
+export function defineConsts(consts) {
+  const rtn = {};
+  for (const [key, value] of Object.entries(consts)) {
+    rtn[key] = value;
+    rtn[key + '__const'] = true;
+  }
+  return rtn;
+}
+
+export function defineInternalConsts(consts) {
+  const rtn = defineConsts(consts);
+  for (const key of Object.keys(consts)) {
+    rtn[key + '__internal'] = true;
+  }
+  return rtn;
+}
+
 export function readFile(filename) {
   return fs.readFileSync(filename, 'utf8');
 }
@@ -385,6 +404,8 @@ export function runInMacroContext(code, options) {
 addToCompileTimeContext({
   assert,
   decoratorSuffixes,
+  defineConsts,
+  defineInternalConsts,
   error,
   isDecorator,
   isJsOnlySymbol,
diff --git a/test/codesize/test_codesize_minimal_O0.expected.js b/test/codesize/test_codesize_minimal_O0.expected.js
index e82c6c5015078..4e920466dca16 100644
--- a/test/codesize/test_codesize_minimal_O0.expected.js
+++ b/test/codesize/test_codesize_minimal_O0.expected.js
@@ -798,6 +798,8 @@ Module['FS_createPreloadedFile'] = FS.createPreloadedFile;
   'convertI32PairToI53',
   'convertI32PairToI53Checked',
   'convertU32PairToI53',
+  'INT53_MAX',
+  'INT53_MIN',
   'bigintToI53Checked',
   'stackAlloc',
   'getTempRet0',
@@ -966,8 +968,6 @@ missingLibrarySymbols.forEach(missingLibrarySymbol)
   'wasmExports',
   'writeStackCookie',
   'checkStackCookie',
-  'INT53_MAX',
-  'INT53_MIN',
   'HEAP8',
   'HEAPU8',
   'HEAP16',
diff --git a/test/codesize/test_unoptimized_code_size.json b/test/codesize/test_unoptimized_code_size.json
index 49629a20e7232..ccf56fa409a36 100644
--- a/test/codesize/test_unoptimized_code_size.json
+++ b/test/codesize/test_unoptimized_code_size.json
@@ -8,9 +8,9 @@
   "no_asserts.wasm": 11389,
   "no_asserts.wasm.gz": 5645,
   "strict.js": 49944,
-  "strict.js.gz": 15826,
+  "strict.js.gz": 15827,
   "strict.wasm": 14275,
   "strict.wasm.gz": 7096,
   "total": 164771,
-  "total_gz": 60319
+  "total_gz": 60320
 }
diff --git a/test/test_jslib.py b/test/test_jslib.py
index 759a61209a589..89ded9366bfbb 100644
--- a/test/test_jslib.py
+++ b/test/test_jslib.py
@@ -1032,3 +1032,77 @@ def test_duplicate_jslib_exports(self, args):
       js = read_file('main.js')
       self.assertEqual(js.count("Module['decoratedExport'] = decoratedExport;"), 1)
       self.assertEqual(js.count("Module['runtimeExport'] = runtimeExport;"), 1)
+
+  @parameterized({
+    '': ([],),
+    'full_export_all': (['-sINCLUDE_FULL_LIBRARY', '-sEXPORT_ALL'],),
+    'O3': (['-O3'],),
+    'closure': (['--closure=1'],),
+  })
+  def test_jslib_const(self, args):
+    create_file('lib.js', r'''
+      addToLibrary({
+        $CONST_A__const: true,
+        $CONST_A: 10,
+        ...defineConsts({
+          $CONST_B: 22,
+          $UNUSED_CONST: 99,
+        }),
+        ...defineInternalConsts({
+          $CONST_C: 10,
+          $UNUSED_INTERNAL_CONST: 99,
+        }),
+        get_const_sum: () => CONST_A + CONST_B + CONST_C,
+      });
+    ''')
+    create_file('src.c', r'''
+      #include <assert.h>
+      #include <stdio.h>
+      int get_const_sum(void);
+      int main() {
+        assert(get_const_sum() == 42);
+        printf("done\n");
+        return 0;
+      }
+    ''')
+    self.do_runf('src.c', 'done\n', cflags=['--js-library', 'lib.js'] + args)
+    js = read_file('src.js')
+    if '-O3' in args or '--closure=1' in args:
+      self.assertNotContained('const CONST_A', js)
+      self.assertNotContained('const CONST_B', js)
+      self.assertNotContained('const CONST_C', js)
+    else:
+      self.assertContained('const CONST_A = 10;', js)
+      self.assertContained('const CONST_B = 22;', js)
+      self.assertContained('const CONST_C = 10;', js)
+    self.assertNotContained('const UNUSED_CONST', js)
+    self.assertNotContained('UNUSED_INTERNAL_CONST', js)
+    self.assertNotContained("Module['CONST_A']", js)
+
+  def test_jslib_const_errors(self):
+    create_file('lib.js', r'''
+      addToLibrary({
+        $bad_func__const: true,
+        $bad_func: () => 42,
+      });
+    ''')
+    self.assert_fail([EMCC, test_file('hello_world.c'), '-sDEFAULT_LIBRARY_FUNCS_TO_INCLUDE=$bad_func', '--js-library', 'lib.js'],
+                     "error: JS library error: '__const' decorator cannot be used with functions: '$bad_func'")
+
+    create_file('lib.js', r'''
+      addToLibrary({
+        $bad_semi__const: true,
+        $bad_semi: ';bad_semi = 42;',
+      });
+    ''')
+    self.assert_fail([EMCC, test_file('hello_world.c'), '-sDEFAULT_LIBRARY_FUNCS_TO_INCLUDE=$bad_semi', '--js-library', 'lib.js'],
+                     "error: JS library error: '__const' decorator cannot be used with ';'-prefixed snippets: '$bad_semi'")
+
+    create_file('lib.js', r'''
+      addToLibrary({
+        $bad_undef__const: true,
+        $bad_undef: undefined,
+      });
+    ''')
+    self.assert_fail([EMCC, test_file('hello_world.c'), '-sDEFAULT_LIBRARY_FUNCS_TO_INCLUDE=$bad_undef', '--js-library', 'lib.js'],
+                     "error: JS library error: '__const' decorator cannot be used with undefined symbols: '$bad_undef'")
diff --git a/tools/link.py b/tools/link.py
index 9b817534cd5fd..ab35f9d598d56 100644
--- a/tools/link.py
+++ b/tools/link.py
@@ -485,6 +485,11 @@ def setup_pthreads():
     '$PThread',
     '$establishStackSpace',
     '$invokeEntryPoint',
+    '$CMD_LOAD',
+    '$CMD_LOADED',
+    '$CMD_CALL_HANDLER',
+    '$CMD_RUN',
+    '$CMD_CHECK_MAILBOX',
   ]
 
   if settings.MINIMAL_RUNTIME:
@@ -1594,6 +1599,8 @@ def limit_incoming_module_api():
 
   if settings.PTHREADS or settings.WASM_WORKERS:
     settings.IMPORTED_MEMORY = 1
+    if settings.ENVIRONMENT_MAY_BE_NODE and not settings.WASM_ESM_INTEGRATION:
+      settings.DEFAULT_LIBRARY_FUNCS_TO_INCLUDE.append('$CMD_UNCAUGHT_EXN')
 
   set_initial_memory()