Use Number.isNaN instead

Author: GarboMuffin

src/compiler/jsexecute.js

@@ -226,13 +226,11 @@ runtimeFunctions.retire = `const retire = () => {
 /**
  * Converts NaN to zero. Used to match Scratch's string-to-number.
  * Unlike (x || 0), -0 stays as -0 and is not converted to 0.
- * This function is written in this specific way to make it easy for browsers to inline.
- * We've found that calling isNaN() causes slowdowns in Firefox, so instead we utilize the
- * fact that NaN is the only JavaScript value that does not equal itself.
+ * This function needs to be written such that it's very easy for browsers to inline it.
  * @param {number} value A number. Might be NaN.
  * @returns {number} A number. Never NaN.
  */
-runtimeFunctions.toNotNaN = `const toNotNaN = value => value === value ? value : 0`;
+runtimeFunctions.toNotNaN = `const toNotNaN = value => Number.isNaN(value) ? 0 : value`;
 
 /**
  * Scratch cast to boolean.