Your code compiles into this when targeting es5:
var SuperArray = (function (_super) {
__extends(SuperArray, _super);
function SuperArray() {
var items = [];
for (var _i = 0; _i < arguments.length; _i++) {
items[_i] = arguments[_i];
}
return _super.apply(this, items) || this;
}
SuperArray.prototype.clear = function () {
while (this.length > 0) {
this.pop();
}
};
return SuperArray;
}(Array));
var array = new SuperArray("Matt", "Mark", "Luke", "John");
array.clear();
It's not possible to extend native objects like that, which is why you're getting this error.
If you'll target es6 then the compiled js will look like this:
class SuperArray extends Array {
constructor(...items) {
super(...items);
}
clear() {
while (this.length > 0) {
this.pop();
}
}
}
var array = new SuperArray("Matt", "Mark", "Luke", "John");
array.clear();
And that will work just fine (if you run it in a browser that supports es6 classes).
Edit
I'll just paste parts of the article Subclassing builtins in ECMAScript 6 which explains why it can't be done with es5:
Allocation obstacle: MyArray allocates the wrong kind of object
Array instances are special – the ECMAScript 6 specification calls
them exotic. Their handling of the property length can’t be replicated
via normal JavaScript. If you invoke the constructor MyArray then an
instance of MyArray is created, not an exotic object.
Initialization obstacle: MyArray can’t use Array for initialization
It is impossible to hand an existing object to Array via this – it
completely ignores its this and always creates a new instance.
