Declaring multiple variables in JavaScript

Question

In JavaScript, it is possible to declare multiple variables like this:

var variable1 = "Hello, World!";
var variable2 = "Testing...";
var          


        

Answer 1

My only, yet essential, use for a comma is in a for loop:

for (var i = 0, n = a.length; i < n; i++) {
  var e = a[i];
  console.log(e);
}

I went here to look up whether this is OK in JavaScript.

Even seeing it work, a question remained whether n is local to the function.

This verifies n is local:

a = [3, 5, 7, 11];
(function l () { for (var i = 0, n = a.length; i < n; i++) {
  var e = a[i];
  console.log(e);
}}) ();
console.log(typeof n == "undefined" ?
  "as expected, n was local" : "oops, n was global");

For a moment I wasn't sure, switching between languages.