CODEWITHSUNDEEP
javascript
Norman
Norman

Reputation: 795

Difference between window[] and eval() - Javascript

I've been using both in javascript ... really don't know the difference. Googling always shows results for the "window object" or "opening a new window in javascript" so couldn't find anything there.

 eval("v"+e)
 window["v"+e]

Sometimes window works for me and at other times eval works ....

So what's the difference between eval() and window[] ?

Sorry for the newbie question though !

Norman

Upvotes: 11

Views: 22172

Answers (4)

Christian C. Salvadó
Christian C. Salvadó

Reputation: 827436

Another point that has not been addressed is that eval will resolve the variable reference using the caller variable environment, for example:

var foo = "global";

(function () {
  var foo = "local";
  alert(eval("foo")); // alerts "local"
  alert(window["foo"]); // alerts "global"
})();

So as you can see, is not completely equivalent.

If you simply want to reference a global variable, I would recommend you to use the window[prop] approach and avoid surprises.

Upvotes: 15

mykhal
mykhal

Reputation: 19905

"v"+e -> string

eval(x) -> evaluates the string x, containing javascript expression

window[x] -> returns window's property with the same name, as tha value of x is. this in fact can be a global variable

therefore, when you have a global variable v1 = "foo", and e = 1, then eval("v"+e) and window["v" + e] both return "foo"

Upvotes: 4

Marimuthu Madasamy
Marimuthu Madasamy

Reputation: 13531

Both return a global variable's value. The difference is that if the global variable is undefined, you will get an error on executing eval() whereas window['variableName'] will return undefined(not an error) because accessing an undefined property is not an error but accessing an undefined variable is an error.

Upvotes: 5

Paul Grime
Paul Grime

Reputation: 15104

eval() interprets arbitrary javascript statements, whereas with window you are accessing a property of the window object.

In your example, you seem to be using a property name in both eval() and window[]. As the global scope in a browser is the same as the window object's scope they will evaluate to the same thing.

You can think of your eval("v"+e) statement as being equivalent to eval("window['v'" + e +" ]").

Upvotes: 7

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