Subclassing Javascript Arrays. TypeError: Array.prototype.toString is not generic

Question

Is it possible to subclass and inherit from javascript Arrays?

I\'d like to have my own custom Array object that has all the features of an Array, but contains addit

Answer 1

Checkout this. It works as it should in all browsers which support '__proto__'.

var getPrototypeOf = Object.getPrototypeOf || function(o){
    return o.__proto__;
};
var setPrototypeOf = Object.setPrototypeOf || function(o, p){
    o.__proto__ = p;
    return o;
};

var CustomArray = function CustomArray() {
    var array;
    var isNew = this instanceof CustomArray;
    var proto = isNew ? getPrototypeOf(this) : CustomArray.prototype;
    switch ( arguments.length ) {
        case 0: array = []; break;
        case 1: array = isNew ? new Array(arguments[0]) : Array(arguments[0]); break;
        case 2: array = [arguments[0], arguments[1]]; break;
        case 3: array = [arguments[0], arguments[1], arguments[2]]; break;
        default: array = new (Array.bind.apply(Array, [null].concat([].slice.call(arguments))));
    }
    return setPrototypeOf(array, proto);
};

CustomArray.prototype = Object.create(Array.prototype, { constructor: { value: CustomArray } });
CustomArray.prototype.append = function(var_args) {
    var_args = this.concat.apply([], arguments);        
    this.push.apply(this, var_args);

    return this;
};
CustomArray.prototype.prepend = function(var_args) {
    var_args = this.concat.apply([], arguments);
    this.unshift.apply(this, var_args);

    return this;
};
["concat", "reverse", "slice", "splice", "sort", "filter", "map"].forEach(function(name) {
    var _Array_func = this[name];
    CustomArray.prototype[name] = function() {
        var result = _Array_func.apply(this, arguments);
        return setPrototypeOf(result, getPrototypeOf(this));
    }
}, Array.prototype);

var array = new CustomArray(1, 2, 3);
console.log(array.length, array[2]);//3, 3
array.length = 2;
console.log(array.length, array[2]);//2, undefined
array[9] = 'qwe';
console.log(array.length, array[9]);//10, 'qwe'
console.log(array+"", array instanceof Array, array instanceof CustomArray);//'1,2,,,,,,,,qwe', true, true

array.append(4);
console.log(array.join(""), array.length);//'12qwe4', 11