Question

I know the possibility to call a function with an array of arguments with apply(obj,args);
Is there a way to use this feature when creating a new instance of a function?

I mean something like this:

function A(arg1,arg2){
    var a = arg1;
    var b = arg2;
}

var a = new A.apply([1,2]); //create new instance using an array of arguments

I hope you understand what i mean… ^^^

Thanks for your help!

Solved!

I got the right answer. To make the answer fit to my question:

function A(arg1,arg2) {
    var a = arg1;
    var b = arg2;
}

var a = new (A.bind.apply(A,[A,1,2]))();

Answer 1

var wrapper = function(f, args) {
    return function() {
        f.apply(this, args);
    };
};

function Constructor() {
    this.foo = 4;
}
var o = new (wrapper(Constructor, [1,2]));
alert(o.foo);

We take a function and arguments and create a function that applies the arguments to that function with the this scope.

Then if you call it with the new keyword it passes in a new fresh this and returns it.

The important thing is the brackets

new (wrapper(Constructor, [1,2]))

Calls the new keyword on the function returned from the wrapper, where as

new wrapper(Constructor, [1,2])

Calls the new keyword on the wrapper function.

The reason it needs to be wrapped is so that this that you apply it to is set with the new keyword. A new this object needs to be created and passed into a function which means that you must call .apply(this, array) inside a function.

Live example

Alternatively you could use ES5 .bind method

var wrapper = function(f, args) {
    var params = [f].concat(args);
    return f.bind.apply(f, params);
};

See example