Emulate array methods of javascript. Object Oriented Javascript by Stoyan Stefanov

Question

I came across book Object Oriented Javascript by Stoyan Stefanov. There is one exercise as below.

Exercise: Imagine Array() doesn't exist and the array literal notation doesn't exist either. Create a constructor called MyArray() that behaves as close to Array() as possible.

I have managed this much but push is not working. Can anybody guide me here?

function MyArray() {
    var arg = arguments;
    this.toString = function () {
        var string = arg[0];
        for (var i = 1; i < arg.length; i++) {
            string += "," + arg[i];
        }
        return string;
    }
    this.length = arg.length;
    this.push = function(p) {
        var a = this.toString() + ",";
        arg[this.length] = p;
        return a.concat(p);
    }
    this.pop = function() {
        return arg[this.length - 1];
    }
    this.join = function (j) {
        var strJoin = arg[0];
        for (var i = 1; i < arg.length; i++) {
            strJoin += j + arg[i];
        }
        return strJoin;
    }
}

var a = new MyArray(1, 2, 3, "test");
console.log(a.toString()); // 1,2,3,test 
console.log(a.length); // 4
console.log(a.push('boo')); // should return 5
console.log(a.toString()); // should return 1,2,3,test,boo
console.log(a.pop()); // boo
console.log(a.join(',')); // 1,2,3,test
console.log(a.join(' isn\'t ')); // 1 isn't 2 isn't 3 isn't test

jsfiddle: http://jsfiddle.net/creativevilla/prf3s/

Why are you using arguments directly? I believe what the author means here is to have you create a LinkedList or some similar data structure. — simonzack
– simonzack, Commented Sep 16, 2013 at 9:59
your pop is actually peek... In short, you keep neglecting to keep the length property updated. — John Dvorak
– John Dvorak, Commented Sep 16, 2013 at 10:01
@JanDvorak: I am not sure how to do this. Can you guide me here — Samrat
– Samrat, Commented Sep 16, 2013 at 10:02

RobH · Accepted Answer · 2013-09-16 10:26:12Z

1

Here's your fixed implementations of push and pop:

this.push = function() {
    // edit - push needs to accept more than one new item.
    for (var i = 0; i < arguments.length; i++) {
        arg[arg.length++] = arguments[i];
    }
    return arg.length;
}
this.pop = function() {
    return arg[--arg.length];
}

Fiddle: http://jsfiddle.net/prf3s/2/

As an aside, I think using the arguments object (which is pretty array like) as the internal data store might be a bit cheating.

edited Sep 16, 2013 at 10:26

answered Sep 16, 2013 at 10:18

RobH

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2 Comments

Samrat Over a year ago

Thanks mate. Just the code i was looking for. Also what do you mean As an aside, I think using the arguments object (which is pretty array like) as the internal data store might be a bit cheating. I shouldn't use that?

RobH Over a year ago

Well you're basically bolting your own class on to the arguments object which already supports access by index and has a length property. Obviously, it's the simplest way to solve the problem and it doesn't actually violate the rules... So I guess it's fine.

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