Object.create vs (evil) eval for creating an object of different types according to the arguments received.

factory.js

function createObject (clazz, args) {
  var o;
  if (Object.create) {
    o = Object.create(clazz)
    clazz.constructor.apply(xx, args);
  } else {
    // screwed! nothing other than evil-eval :-(
    o = eval("new " + clazz.constructor.name + "(" + args + ")");
  }
}

why-factory.js

function A(x, y) {
    this.x = x;
    this.y = y
}

function B(x, y, z) {
    this.x = x;
    this.y = y;
    this.z = z;
}

// ... in actual case you will be getting the args dynamically, as well as sometimes the prototype too.
var clazzName = 'A'
var args = [1,2];

var xx;
// this is the old (evil) way.
xx = /*evil*/eval('new ' + clazzName + '(' + args + ')');

console.log(xx);

// this is the factory way; cleaner and, better way
var Clazz = window[clazzName];
xx = Object.create(Clazz.prototype)
Clazz.apply(xx, args);

console.log(xx);

Here it is shown how it is possible to create an object with arbitrary arguments without the evil eval.

Disclaimer: This file is for educational purpose only, original may vary.