Object type determined at runtime - Javascript (ExtJS)

Question

Hi All,

This may not be possible (or might be dead easy! :) ) so here it is...

I want to be able to create objects of a type that is dependant on a variable set, without the need for a big switch statement.

I think it is possible in PHP to do something like...

$objectType = "myNewClass";
$newObject = new $objectType();

where the $newObject variable will hold an instance of the Class "myNewClass".

Is this (or any similar technique) possible with Javascript?

Thanks Stuart

Answer 1

If your constructor functions are defined in the global scope, you can access it trough the bracket notation (window[fnName]):

function ObjectType1(){  // example constructor function
  this.type = 1;
}


var objectType = 'ObjectType1'; // string containing the constructor function name

var obj = new window[objectType](); // creating a new instance using the string
                                    // variable to call the constructor

See: Member Operators

Answer 2

Should be doable using eval():

var obj = eval("new " + objectType + "()");

Answer 3

CMS's answer is good, but in EXT you're probably dealing with namespaces.

I create an object map that holds any dynamic classes:

// within a namespace:
var ns = {
    Thinger: function(){}
};

// globals:
var Zinger = function(){} 

// map:
var classes = {
    zinger:Zinger,
    thinger:ns.Thinger    
};

var type = "thinger";

var myClass = new classes[type](props, type, etc);