This is a new technology, part of the ECMAScript 2015 (ES6) standard .
This technology's specification has been finalized, but check the compatibility table for usage and implementation status in various browsers.

Summary

The function.name property returns the name of the function.

Property attributes of Function.name
Writable no
Enumerable no
Configurable yes
Notice that in non-standard, pre-ES6 implementations the configurable attribute was false as well.

Description

The name property returns the name of a function, or an empty string for anonymous functions:

function doSomething() {}

console.log(doSomething.name); // logs "doSomething"

Functions created with the syntax new Function(...) or just Function(...) have their name property set to an empty string. In the following examples anonymous functions are created, so name returns an empty string:

var f = function() {};
var object = {
  someMethod: function() {}
};

console.log(f.name == ''); // true
console.log(object.someMethod.name == ''); // also true

You can define a function with a name in a function expression:

var object = {
  someMethod: function object_someMethod() {}
};
console.log(object.someMethod.name); // logs "object_someMethod"

try { object_someMethod } catch(e) { console.log(e); }
// ReferenceError: object_someMethod is not defined

You cannot change the name of a function, this property is read-only:

var object = {
  // anonymous
  someMethod: function() {}
};

object.someMethod.name = 'someMethod';
console.log(object.someMethod.name); // empty string, someMethod is anonymous

To change it, you could use Object.defineProperty though.

Examples

You can use obj.constructor.name to check the "class" of an object:

function a() {}

var b = new a();

console.log(b.constructor.name); // logs "a"

Specifications

Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'name' in that specification.
Standard Initial definition.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 33 (Yes) Not supported (Yes) (Yes)
Configurable: true 43 38 (38) ? ? ?
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support (Yes) (Yes) (Yes) Not supported (Yes) (Yes)
Configurable: true ? ? 38.0 (38) ? ? ?

Document Tags and Contributors

Last updated by: bergus,