What's wrong with this code? I'm trying to extend the class foo with all the native array's functions.
function foo(){
Array.call(this);
}
foo.prototype.addFruit=function(item){
this.unshift(item);
}
foo.prototype=new Array();
foo.prototype.constructor=foo;
var c =new foo();
c.addFruit('Apple');
document.write(c.join('-'));
You add the method addFruit to the prototype of foo, then you overwrote the the foo.prototype, so the method is missing (The prototype changed to another object after you put a method to the original prototype).
You should change your order of the code, assign the prototype before add method to prototype.
foo.prototype=new Array();
foo.prototype.constructor=foo;
foo.prototype.addFruit=function(item){
this.unshift(item);
};
You add the addFruit property to the prototype before you overwrite the whole prototype property with a new Array.
Instead of new Array, you should use Object.create(Array.prototype) so you don't have an actual Array instance as the prototype (with length etc) but only an object inheriting from the Array prototype.
Array.call(this) unfortunately does not work. It returns a new array, which is assigned to nothing, but it does not do anything on this. You can check by this !== Array.call(this). Actually, it is not possible to "subclass" Array - read on http://perfectionkills.com/how-ecmascript-5-still-does-not-allow-to-subclass-an-array
foo.prototype === Array.prototype, while Object.create creates a new object with a properly set-up prototype chain.