how to pass in a class name as variable using javascript

Question

How can I pass in a class name as a variable using javascript?

Let's say I have the class Person.

I want to pass in the name of the class to a function so that that function can call that class.

so the function is

function openClass(name)

I want to pass in

openClass('person')

so that openClass can call the class person

for example

function openClass(name)
{
    return new name() // here I want this line to actually 
                      // call the class "Person" if that is 
                      // what is passed in as a name parameter,

}

since classes are just functions, this is a duplicate of How to execute a JavaScript function when I have its name as a string — jbabey
– jbabey, Commented Nov 7, 2012 at 16:07

Matt Greer · Accepted Answer · 2012-11-07 16:00:01Z

7

Technically, there are no classes in JavaScript. Although many third party libraries do create a class system on top of JavaScript.

The "class" is typically a constructor function. So if you have the name of the function, it's a matter of digging it out of the global scope. Assuming the function is defined globally:

var Constructor = window[name];
return new Constructor();

If your function is actually defined at say my.namespace.Person, then it's a bit more complicated, but still the same general idea.

answered Nov 7, 2012 at 16:00

Matt Greer

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2 Comments

Matt Greer Over a year ago

Also assuming window is the global object. It isn't always (say in node.js for example)

Matt Greer Over a year ago

People seem to be downvoting this approach (see dystroy's answer too), curious why

Denys Séguret · Accepted Answer · 2012-11-07 16:00:32Z

3

You can do

function openClass(name) {
    return new window[name]();
}

Demonstration (open the console)

Of course, if you don't declare your class as a global function but in a specific object or array, just replace window by this object or array.

answered Nov 7, 2012 at 16:00

Denys Séguret

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Comments

Ben McCormick · Accepted Answer · 2012-11-07 16:02:37Z

2

You can just pass the constructor of that class. So if the class is Person, it will have a constructor

var Person = function(){
    //...
}

you can pass that in to getClass as an argument

var getClass = function(constructor){
    return new constructor()
};

var newObject = getClass(Person);

answered Nov 7, 2012 at 16:02

Ben McCormick

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Comments

Kendall Frey · Accepted Answer · 2012-11-07 15:59:48Z

-3

Simply call openClass(Person).

That passes the Person function into openClass, where it can be called normally.

If you really need to pass it as a string, then you can look for the Person function by name:

window[name]

answered Nov 7, 2012 at 15:59

Kendall Frey

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1 Comment

Vithozor Over a year ago

Oh, that's curious, all the responses had one downvote except this one...you need to do that with 12.7k reputation?

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