[sbc100]

In #24116, a loop was added at the end of src/lib/libfs.js to generate $FS_<symbol> wrapper functions ((...args) => FS.foo(...)) for FS API methods. While the comment noted that non-functions should be skipped, the condition only checked key[0] !== key[0].toLowerCase() (which filters out uppercase classes like ErrnoError, FSStream, and FSNode), assuming all lowercase properties on LibraryFS.$FS were functions.

In practice, LibraryFS.$FS also contains lowercase state and object properties (root, mounts, devices, streams, nextInode, nameTable, currentPath, initialized, ignorePermissions, syncFSRequests, and chrdev_stream_ops). Wrapping these in (...args) => FS.<key>(...args) is broken:

• Calling any of these generated aliases at runtime would unconditionally throw TypeError: FS.<key> is not a function.
• When compiling with -sINCLUDE_FULL_LIBRARY and --closure=1 (such as with -sEXPORT_ES6), Closure Compiler rejects calls to these non-callable properties on FS.
• In unoptimized (-O0 / ASSERTIONS) builds, these bogus symbols pollute missingLibrarySymbols, unnecessarily increasing JS code size.

Check typeof LibraryFS.$FS[key] !== 'function' alongside the existing lowercase check so that only actual methods on FS receive function aliases.

Split out from #27747

[gemini-code-assist]

Code Review

This pull request updates src/lib/libfs.js to prevent creating aliases for non-function properties of LibraryFS.$FS by verifying that the property is a function. This optimization reduces the overall code size, which is reflected in the updated code size test files and expectations. There are no review comments, so I have no feedback to provide.