Function: name
BaselineWidely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since August 2016.
Thename data property of aFunction instance indicates the function's name as specified when it was created, or it may be eitheranonymous or'' (an empty string) for functions created anonymously.
Try it
const func1 = function () {};const object = { func2: function () {},};console.log(func1.name);// Expected output: "func1"console.log(object.func2.name);// Expected output: "func2"Value
A string.
Property attributes ofFunction: name | |
|---|---|
| Writable | no |
| Enumerable | no |
| Configurable | yes |
Note:In non-standard, pre-ES2015 implementations theconfigurable attribute wasfalse as well.
Description
The function'sname property can be used to identify the function in debugging tools or error messages. It has no semantic significance to the language itself.
Thename property is read-only and cannot be changed by the assignment operator:
function someFunction() {}someFunction.name = "otherFunction";console.log(someFunction.name); // someFunctionTo change it, useObject.defineProperty().
Thename property is typically inferred from how the function is defined. In the following sections, we will describe the various ways in which it can be inferred.
Function declaration
Thename property returns the name of a function declaration.
function doSomething() {}doSomething.name; // "doSomething"Default-exported function declaration
Anexport default declaration exports the function as a declaration instead of an expression. If the declaration is anonymous, the name is"default".
// -- someModule.js --export default function () {}// -- main.js --import someModule from "./someModule.js";someModule.name; // "default"Function constructor
Functions created with theFunction() constructor have name "anonymous".
new Function().name; // "anonymous"Function expression
If the function expression is named, that name is used as thename property.
const someFunction = function someFunctionName() {};someFunction.name; // "someFunctionName"Anonymous function expressions, created using either thefunction keyword or the arrow function syntax, have"" (an empty string) as their name by default.
(function () {}).name; // ""(() => {}).name; // ""However, such cases are rare — usually, in order to call the function elsewhere, the function expression is associated with an identifier. The name of an anonymous function expression can be inferred within certain syntactic contexts, including:variable declaration, method,initializer, and default value.
One practical case where the name cannot be inferred is a function returned from another function:
function getFoo() { return () => {};}getFoo().name; // ""Variable declaration and method
Variables and methods can infer the name of an anonymous function from its syntactic position.
const f = function () {};const object = { someMethod: function () {},};console.log(f.name); // "f"console.log(object.someMethod.name); // "someMethod"The same applies to assignment:
let f;f = () => {};f.name; // "f"Initializer and default value
Functions in initializers (default values) ofdestructuring,default parameters,class fields, etc., will inherit the name of the bound identifier as theirname.
const [f = () => {}] = [];f.name; // "f"const { someMethod: m = () => {} } = {};m.name; // "m"function foo(f = () => {}) { console.log(f.name);}foo(); // "f"class Foo { static someMethod = () => {};}Foo.someMethod.name; // someMethodShorthand method
const o = { foo() {},};o.foo.name; // "foo";Bound function
Function.prototype.bind() produces a function whose name is "bound " plus the function name.
function foo() {}foo.bind({}).name; // "bound foo"Getter and setter
Class
A class's name follows the same algorithm as function declarations and expressions.
class Foo {}Foo.name; // "Foo"Warning:JavaScript will set the function'sname property only if a function does not have an own property calledname. However, classes'static members will be set as own properties of the class constructor function, and thus prevent the built-inname from being applied. Seean example below.
Symbol as function name
If aSymbol is used a function name and the symbol has a description, the method's name is the description in square brackets.
const sym1 = Symbol("foo");const sym2 = Symbol();const o = { [sym1]() {}, [sym2]() {},};o[sym1].name; // "[foo]"o[sym2].name; // "[]"Private fields and methods
Private fields and private methods have the hash (#) as part of their names.
class Foo { #field = () => {}; #method() {} getNames() { console.log(this.#field.name); console.log(this.#method.name); }}new Foo().getNames();// "#field"// "#method"Examples
Telling the constructor name of an object
You can useobj.constructor.name to check the "class" of an object.
function Foo() {} // Or: class Foo {}const fooInstance = new Foo();console.log(fooInstance.constructor.name); // "Foo"However, because static members will become own properties of the class, we can't obtain the class name for virtually any class with a static method propertyname():
class Foo { constructor() {} static name() {}}With astatic name() methodFoo.name no longer holds the actual class name but a reference to thename() function object. Trying to obtain the class offooInstance viafooInstance.constructor.name won't give us the class name at all, but instead a reference to the static class method. Example:
const fooInstance = new Foo();console.log(fooInstance.constructor.name); // ƒ name() {}Due to the existence of static fields,name may not be a function either.
class Foo { static name = 123;}console.log(new Foo().constructor.name); // 123If a class has a static property calledname, it will also becomewritable. The built-in definition in the absence of a custom static definition isread-only:
Foo.name = "Hello";console.log(Foo.name); // "Hello" if class Foo has a static "name" property, but "Foo" if not.Therefore you may not rely on the built-inname property to always hold a class's name.
JavaScript compressors and minifiers
Warning:Be careful when using thename property with source-code transformations, such as those carried out by JavaScript compressors (minifiers) or obfuscators. These tools are often used as part of a JavaScript build pipeline to reduce the size of a program prior to deploying it to production. Such transformations often change a function's name at build time.
Source code such as:
function Foo() {}const foo = new Foo();if (foo.constructor.name === "Foo") { console.log("'foo' is an instance of 'Foo'");} else { console.log("Oops!");}may be compressed to:
function a() {}const b = new a();if (b.constructor.name === "Foo") { console.log("'foo' is an instance of 'Foo'");} else { console.log("Oops!");}In the uncompressed version, the program runs into the truthy branch and logs "'foo' is an instance of 'Foo'" — whereas, in the compressed version it behaves differently, and runs into the else branch. If you rely on thename property, like in the example above, make sure your build pipeline doesn't change function names, or don't assume a function has a particular name.
Specifications
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-function-instances-name |