determining the type of a javascript object instance

Question

Is it possible to determine the type of a JavaScript object?

See the example below for more context:

var Cat = function() {this.numEyes=2;this.numLegs=4};
var c = new Cat();

How do we determine the type of c.

I am not looking for

(c instanceof Cat)

Essentially how would I get the string Cat given c.

dup http://stackoverflow.com/questions/332422/how-do-i-get-the-name-of-an-objects-type-in-javascript — georg, Dec 11 '13 at 13:35

score 0 · Answer 1 · answered Dec 11 '13 at 13:30

0

I think you are after the constructor name and not the type. Problem is the way you defined it will not work.

var Cat = function (){}; 
var c = new Cat(); 
console.log(c.constructor.name);  //""

If you name your function, you can get the name

var Dog = function Dog(){}; 
var d = new Dog(); 
console.log(d.constructor.name);  //Dog

answered Dec 11 '13 at 13:30

epascarello

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As a note, this does not work in IE (no `name` property support). – GOTO 0 Dec 11 '13 at 13:32

score 0 · Accepted Answer · edited May 23 '17 at 11:49

In the original post formulation still visible in the revision history, Cat was defined without var, i.e.:

Cat = function() {this.numEyes=2;this.numLegs=4};

In this case, the constructor's name can be determined by iterating over the properties of the global object (window for browsers).

Cat = function() {this.numEyes=2;this.numLegs=4};
var c = new Cat();
alert(typeNameOf(c));

function typeNameOf(c) {
    for (name in window) {
        if (window[name] == Object.getPrototypeOf(c).constructor) return name;
    }
}

This should alert "Cat" in all modern browsers.

determining the type of a javascript object instance

2 Answers2