A function to create a new object using a constructor function when you only have an array of arguments, analogous to how you would use "apply" to call a function, but for "new".

make.js

// A function to create a new object using a constructor function when you only 
// have an array of arguments, analogous to how you would use "apply" to call a
// function, but for "new".

function make(C, args) {
    function T(){
        C.apply(this, args);
    }
    T.prototype = C.prototype;
    return new T();
}

// Example usage:

function F(a, b) {
    this.a = a;
    this.b = b;
}

F.prototype.foo = function(){console.log('foo');};

var o = make(F,[1,2]);

// Check we created the same object as we would have with var o = new F(1, 2);
console.log(o.a); // 1
console.log(o.b); // 2
o.foo(); // 'foo'
console.log(o.constructor == F); // true

Note an ES5 version, such as

function make(C, args) {
  return new (Function.prototype.bind.apply(C, [null].concat(args)));
};

works even on functions that have different call and construct behaviour, such as String Date etc. - see https://twitter.com/littlecalculist/status/330757690743746561