CODEWITHSUNDEEP
javascript
theJava
theJava

Reputation: 15034

usage of call method and Array.prototype.slice.call

if (!Function.prototype.bind) {
  Function.prototype.bind = function (oThis) {
    if (typeof this !== "function") {
      // closest thing possible to the ECMAScript 5 internal IsCallable function
      throw new TypeError("Function.prototype.bind - what is trying to be bound is not callable");
    }

    var aArgs = Array.prototype.slice.call(arguments, 1), 
        fToBind = this, 
        fNOP = function () {},
        fBound = function () {
          return fToBind.apply(this instanceof fNOP && oThis
                                 ? this
                                 : oThis,
                               aArgs.concat(Array.prototype.slice.call(arguments)));
        };

    fNOP.prototype = this.prototype;
    fBound.prototype = new fNOP();

    return fBound;
  };
}

I was looking at the source of the bind function, i was just thinking on why they are doing an Array.prototype.slice.call when i can directly do a slice to my arguments.

Upvotes: 0

Views: 229

Answers (1)

VisioN
VisioN

Reputation: 145398

Because arguments is not a pure JavaScript array, but array-like object. So in order to make changes to it, you have to transform it to the real array using Array.prototype.slice.call.

From MDN:

The arguments object is not an Array. It is similar to an Array, but does not have any Array properties except length.

Upvotes: 2

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