Function.name

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

Description

The name property returns the name of a function, or (before ES6 implementations) 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

Browsers that implement ES6 functions can infer the name of an anonymous function from its syntactic position. For example:

var f = function() {};
console.log(f.name); // "f"

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 (read the warnings below):

function Foo() {}  // ES2015 Syntax: class Foo {}

var foo = new Foo();
console.log(foo.constructor.name); // logs "Foo"

class Foo {
  constructor() {}
  static name() {}
}
var foo = new Foo();
console.log(foo.constructor.name); // logs function name()

// Name of constructor function Foo is no longer read-only
Foo.name = "Hello";
console.log(foo.constructor.name); // logs "Hello"

function Foo() {}
Object.defineProperty(Foo, "name", { writable: true });
Foo.name = function() { 
   return "Hello"; 
};
var foo = new Foo();
console.log(Foo.constructor.name);

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

if (foo.constructor.name === "Foo") {
  console.log("'foo' is an instance of 'Foo'");
} else {
  console.log("Oops!");
}

function a() {};
var b = new a();
if (b.constructor.name === "Foo") {
  console.log("'foo' is an instance of 'Foo'");
} else {
  console.log("Oops!");
}

Specifications

Browser compatibility

[1] See bug 883377.