Is non-breaking space always treated like whitespace in Javascript source?

Question

While doing a code review of some Javascript files, my code review tool was showing "�" (missing character symbol) in one of the files. Upon further investigation, it turned out that the developer had used non-breaking spaces in their code. (Probably a result of copy/pasting from web.)

To my surprise, this works fine in Chrome, IE11, and Edge. But I'm concerned that it wouldn't work in all browsers. Is this a required feature of Javascript language that I can rely on? Or is this something I need to tell the developer to fix to avoid potential issues on other browsers?

Here is an example:

//NOTE: All spaces in below code are non-breaking space (0xA0), not space (0x20)
function test() {
  var mystr = 'hello';
  alert(mystr);
}

test();

Answer 1

Yes, no-break spaces are considered whitespace according to the ECMAScript® 2015 Language Specification:

White Space Code Points:

Code Point:   Name:                                   Abbreviation:
------------------------------------------------------------------
U+0009        CHARACTER TABULATION                    <TAB>
U+000B        LINE TABULATION                         <VT>
U+000C        FORM FEED (FF)                          <FF>
U+0020        SPACE                                   <SP>
U+00A0        NO-BREAK SPACE                          <NBSP>
U+FEFF        ZERO WIDTH NO-BREAK SPACE               <ZWNBSP>
Other (Zs)    Any other unicode "Separator, space"    <USP>

Zs refers to code points listed in the "Separator, space" (Zs) category by Unicode 5.1. ECMAScript.

Example code featuring all kinds of whitespace:

// var keyword followed by different kinds of whitespace:
var	tab = "	";
varvt = "";
varff = "";
var sp = " ";
var nbsp = " ";
varzwnbsp = "";
var usp = " ";

console.log("whitespace:", tab, vt, ff, sp, nbsp, zwnbsp, usp);

... is this something I need to tell the developer to fix to avoid potential issues on other browsers?

I recommend using spaces only (some allow tabs) as it prevents all kinds of whitespace mangling by different text editors and readability issues as demonstrated by above code sample.