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up vote 3 down vote favorite

i would like to create a new object in javascript (using simple inheritance) such that the class of the object is defined from a variable:

var class = 'Person';
var inst = new class

any ideas?

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4 Answers

up vote 12 down vote accepted

You can do something like

function Person(){};
var name = 'Person';
var inst = new this[name]

The key is just referencing the object that owns the function that's the constructor. This works fine in global scope but if you're dumping the code inside of a function, you might have to change the reference because this probably wont work.

EDIT: To pass parameters:

function Person(name){alert(name)};
var name = 'Person';
var inst = new this[name]('john')
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+1 very nice meder – alex Apr 30 '11 at 1:46
thanks! how do i pass parameters? – yee379 Apr 30 '11 at 1:48
You can also use apply to pass parameters, which is useful if you don't know them in advance, a.g. this[name].apply(null, args) where args is an array of parameters/arguments. Seems to be the case more often than not when calling functions dynamically. – Jamie Treworgy Apr 30 '11 at 13:19
This solution saved me having to use eval(). Thank you! – Jimmy Breck-McKye Jan 6 at 22:11
up vote 0 down vote

This talk was really helpful when I got into different inheritance patterns in javascript. Example code is included in the second link (the video introduces it).

http://alexsexton.com/?p=94

http://alexsexton.com/inheritance/demo/

http://alexsexton.com/?p=51

HTH

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up vote 0 down vote

Try

function Person(name, age, gender) { //and any other params you need
return {
name: name,
age: age,
gender: gender
}
});
var p = new Person("Billy Bob", "Too Old", "Male???");
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up vote 0 down vote

Here's how I do it. Similar to meder's answer.

var className = 'Person'
// here's the trick: get a reference to the class object itself
// (I've assumed the class is defined in global scope)
var myclass = window[className];
// now you have a reference to the object, the new keyword will work:
var inst = new myclass('params','if','you','need','them');
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