perf(isFloat): cache the compiled regex instead of rebuilding it per call

src/lib/isFloat.js

@@ -2,10 +2,25 @@ import assertString from './util/assertString';
 import isNullOrUndefined from './util/nullUndefinedCheck';
 import { decimal } from './alpha';
 
+// The pattern only varies with the decimal separator, which comes from a fixed set of
+// locales, so the compiled regexes are cached instead of being rebuilt on every call.
+const floatRegexByDecimal = new Map();
+
+function floatRegex(decimalSeparator) {
+  let regex = floatRegexByDecimal.get(decimalSeparator);
+
+  if (!regex) {
+    regex = new RegExp(`^(?:[-+])?(?:[0-9]+)?(?:\\${decimalSeparator}[0-9]*)?(?:[eE][\\+\\-]?(?:[0-9]+))?$`);
+    floatRegexByDecimal.set(decimalSeparator, regex);
+  }
+
+  return regex;
+}
+
 export default function isFloat(str, options) {
   assertString(str);
   options = options || {};
-  const float = new RegExp(`^(?:[-+])?(?:[0-9]+)?(?:\\${options.locale ? decimal[options.locale] : '.'}[0-9]*)?(?:[eE][\\+\\-]?(?:[0-9]+))?$`);
+  const float = floatRegex(options.locale ? decimal[options.locale] : '.');
   if (str === '' || str === '.' || str === ',' || str === '-' || str === '+') {
     return false;
   }