Difference between variable declaration syntaxes in Javascript (including global variables)?

Question

Is there any difference between declaring a variable:

var a=0; //1

...this way:

a=0; //2

...or:

Answer 1

Bassed on the excellent answer of T.J. Crowder: (Off-topic: Avoid cluttering window)

This is an example of his idea:

Html

  
    
    
    
  

  
    
Hello !
      

init.js (Based on this answer)

var MYLIBRARY = MYLIBRARY || (function(){
    var _args = {}; // private

    return {
        init : function(Args) {
            _args = Args;
            // some other initialising
        },
        helloWorld : function(i) {
            return _args[i];
        }
    };
}());

script.js

// Here you can use the values defined in the html as if it were a global variable
var a = "Hello World " + MYLIBRARY.helloWorld(2);

alert(a);

Here's the plnkr. Hope it help !