Is there any difference between declaring a variable:
var a=0; //1
...this way:
a=0; //2
...or:
window.a=0; //3
in global scope?
This question is related to
javascript
<title>Index.html</title>
<script>
var varDeclaration = true;
noVarDeclaration = true;
window.hungOnWindow = true;
document.hungOnDocument = true;
</script>
<script src="external.js"></script>
/* external.js */
console.info(varDeclaration == true); // could be .log, alert etc
// returns false in IE8
console.info(noVarDeclaration == true); // could be .log, alert etc
// returns false in IE8
console.info(window.hungOnWindow == true); // could be .log, alert etc
// returns true in IE8
console.info(document.hungOnDocument == true); // could be .log, alert etc
// returns ??? in IE8 (untested!) *I personally find this more clugy than hanging off window obj
Is there a global object that all vars are hung off of by default? eg: 'globals.noVar declaration'
Keeping it simple :
a = 0
The code above gives a global scope variable
var a = 0;
This code will give a variable to be used in the current scope, and under it
window.a = 0;
This generally is same as the global variable.
Bassed on the excellent answer of T.J. Crowder: (Off-topic: Avoid cluttering window)
This is an example of his idea:
Html
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript" src="init.js"></script>
<script type="text/javascript">
MYLIBRARY.init(["firstValue", 2, "thirdValue"]);
</script>
<script src="script.js"></script>
</head>
<body>
<h1>Hello !</h1>
</body>
</html>
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 !
In global scope there is no semantic difference.
But you really should avoid a=0 since your setting a value to an undeclared variable.
Also use closures to avoid editing global scope at all
(function() {
// do stuff locally
// Hoist something to global scope
window.someGlobal = someLocal
}());
Always use closures and always hoist to global scope when its absolutely neccesary. You should be using asynchronous event handling for most of your communication anyway.
As @AvianMoncellor mentioned there is an IE bug with var a = foo only declaring a global for file scope. This is an issue with IE's notorious broken interpreter. This bug does sound familiar so it's probably true.
So stick to window.globalName = someLocalpointer
Source: Stackoverflow.com