Deleting a window property in IE

Question

I can\'t find any information on this issue; why doesn\'t the following code work in IE?

window.x = 45;
delete window.x;
// or delete window[\'x\'];

Answer 1

I implemented this solution when dealing with caching my own data - the data wasn't much the the frequency of the cache was such that the memory leak might have become an issue. It's costly, but periodically remapping the object was the easiest way for me to be sure it wasn't getting out of hand.

obj = {a: 1, b: 2, c: 3};
var max;

function unset(obj, key) {
    try {
        delete obj[key];
    } catch (e) {
        obj[key] = undefined;
    }

    max++;

    if(max > 200) {
        var keys = Object.keys(obj);
        var len = keys.length;
        var n_obj = {};
        for(var i = 0; i < len; i++) {
            if(obj.hasOwnProperty(keys[i]) && obj[keys[i]] !== undefined) {
                n_obj[keys[i]] = obj[keys[i]];
            }
        }
        return n_obj;
    }
    return obj;
}

obj; //{a: 1, b: 2, c: 3}
obj = unset(obj, "b"); //{a: 1, b: undefined, c: 3} OR {a: 1, c: 3}
//and then eventually we'll garbage collect and...
obj = unset(obj, "b"); //{a: 1, c: 3}   

Hopefully, that's useful to some!

Answer 2

Does this help?

window.x = 45;
alert(window.x);
window.x = null;

I tried this in IE and window.x did have a value, which proves it can be set. Setting the value to null is your best bet for clearing it out.

Answer 3

Gasper made a comment with the solution he finished on, but I think its worth calling out as an actual answer:

try 
{ 
    delete window.x; 
} 
catch(e) 
{ 
    window["x"] = undefined; 
}

Interesting issue, I was just banging my head against it tonight. The exception is thrown on IE but not Firefox. I would suspect this workaround leaks memory, so use sparingly.

It was asked, why not just assign undefined? It matters if you want to enumerate the keys later (though if you're relying on the workaround, the key enumeration still won't do what you want...). But anyhow, to highlight the difference between delete and simply assigning undefined (http://jsfiddle.net/fschwiet/T4akL/):

var deleted = {
    a: 1
};

var cleared = {
    a: 1
};

delete deleted["a"];
cleared["a"] = undefined;

for(var key in deleted) {
    console.log("deleted has key", key);
}

for(var key in cleared) {
    console.log("cleared has key", key);
}

console.log("deleted has a?", deleted.hasOwnProperty('a'));
console.log("cleared has a?", cleared.hasOwnProperty('a'));

produces output:

cleared has key a
deleted has a? false
cleared has a? true 

Answer 4

I would do it this way:

    window[x] = undefined;
    try{
        delete window[x];
    }catch(e){}