How to get a JavaScript Object's Class?

Question

I created a Javascript Obj, but how can I get back the Class of that Javascript Obj?

I want something that similar to Java .getClass() method.

Answer 1

There's no exact counterpart to Java's #getClass() in JavaScript. Mostly that's due to JavaScript being a prototype-based language, as opposed to Java being a class-based one.

Depending on what you need #getClass() for, there are several options in JavaScript:

• typeof()
• instanceof
• func.prototype, proto.isPrototypeOf
• obj.constructor

A few examples:

function Foo() {}
var foo = new Foo()

typeof(foo) // == "object"

foo instanceof Foo // == true
foo.constructor // == Foo

Foo.prototype.isPrototypeOf(foo) // == true
Foo.prototype.bar = function (x) {return x+x}
foo.bar(21) // == 42

Answer 2

Javascript is a class-less languages: there are no classes that defines the behaviour of a class statically as in Java. JavaScript uses prototypes instead of classes for defining object properties, including methods, and inheritance. It is possible to simulate many class-based features with prototypes in JavaScript.

Answer 3

You can get a reference to the constructor function which created the object by using the constructor property:

function MyObject(){
}

var obj = new MyObject();
obj.constructor; // MyObject

If you need to confirm the type of an object at runtime you can use the instanceof operator:

obj instanceof MyObject // true

Answer 4

In javascript, there are no classes but i think you whant the constructor name so obj.constructor.toString() will tell you what you need.

Answer 5

This function returns either "undefined", "null", or the "class" in [object class] from Object.prototype.toString.call(someObject).

function getClass(obj) {
  if (typeof obj === "undefined")
    return "undefined";
  if (obj === null)
    return "null";
  return Object.prototype.toString.call(obj)
    .match(/^\[object\s(.*)\]$/)[1];
}

getClass("")   === "String";
getClass(true) === "Boolean";
getClass(0)    === "Number";
getClass([])   === "Array";
getClass({})   === "Object";
getClass(null) === "null";
// etc...