CODEWITHSUNDEEP
javascript
Marwan
Marwan

Reputation: 2402

can a JavaScript Array be null?

I'm Collecting JavaScript Classes prototypes that make it compatible to old browsers never mind of that but what i wonder while collecting them that the Developer At Mozila comparing the Array to null i can see that is non since but maybe I'm wrong and there is an explanation for that ???

 if (!Array.prototype.every) {
    Array.prototype.every = function(fun /*, thisp */) {
        "use strict";

        if (this == null)
            throw new TypeError();

        var t = Object(this);
        var len = t.length >>> 0;
        if (typeof fun != "function")
            throw new TypeError();

        var thisp = arguments[1];
        for (var i = 0; i < len; i++) {
            if (i in t && !fun.call(thisp, t[i], i, t))
                return false;
        }

        return true;
    };
}

at this line 

 if (this == null)

this is refers to the Array

This code at Mozila

Kindly i need an explanation is that a logic to compare a Array to a null even if i know that "this" which is refer to a must array type not a variable can be array or null ?? what you think ??

Upvotes: 2

Views: 136

Answers (2)

ThiefMaster
ThiefMaster

Reputation: 318468

It could happen when someone calls it without a context, e.g. Array.prototype.every(...) instead of someArray.every(...). Or a more likely case: Passing someArray.every as a callback to some other function which will then invoke it without the proper context.

Since the function is running in Strict Mode this === undefined when no context is provided. And undefined == null.

Upvotes: 4

monshq
monshq

Reputation: 343

It's useful for cases like:

Array.prototype.every.call(null, ...);

You are not likely to meet that version of code, but in place of null can be a variable, that is not yet initialized, for example. In that case TypeError is only logical.

Upvotes: 2

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