Is new line a separator in Javascript

Question

While debugging a web SPA issue, I stumbled on something to which I could not find concrete references online: missing comma separator between function expressions in javascript. Here's the details:

This works - explicit comma as a separator is there (note - intentionally on one line):

var f1 = function() { console.log(1); }, f2 = function() { console.log(2);}

This however doesn't seem to work, trying it in the Chrome console (again - one-liner on purpose):

var f5 = function() { console.log(5); } f6 = function() { console.log(6);} 
VM37860:2 Uncaught SyntaxError: Unexpected identifier
    at Object.InjectedScript._evaluateOn (<anonymous>:895:140)
    at Object.InjectedScript._evaluateAndWrap (<anonymous>:828:34)
    at Object.InjectedScript.evaluate (<anonymous>:694:21)

Then this one seems to work - notice missing comma:

> var f3 = function() { 
   console.log(3); 
  } 
  f4 = function() { 
   console.log(4);
  }
< function f4()
> f4()
  4
< undefined
> f3()
  3
< undefined

I am looking for explanation or a reference to one as to why multi-line but missing comma seems to work.

The ramification was that a missing comma in our source that slipped into the build caused unexpected behavior in otherwise syntax-correct script bundle (the script snippet containing the missing comma piece is bundled together with many other components on the server side and emitted as a single script tag to the browser). I.e. Chrome and FF were not reporting syntax errors, yet script behavior was incorrect (it's a complex knockout.js-based SPA but it seemed as if the wrong function out of many functions with same name, but different scope, was being called; version of knockout used is 2.x).

Regardless - I am interested if someone can explain the console behavior from pure Javascript / Chrome console point of view, outside of the scope of knockout-based SPA.

Answer 1

Javascript will assume semicolons at some line breaks. Ugh. So your second variable was a global, not part of the var. http://inimino.org/~inimino/blog/javascript_semicolons

Answer 2

If you don't use comma, it means "a sentence" at same line. In another line Javascript will assume another sentence. And comma can be used "a lot of variable".

for example, var f1, f2--> var f1; var f2; var f3 = 10 f4 = 20 // it is global variable. it is not same line.`