Web/JavaScript/Reference/Global objects/Function/toString

The toString() method returns a string representing the source code of the function.

Syntax

function.toString()

Return value

A string representing the source code of the function.

Description

The Function object overrides the toString method inherited from Object; it does not inherit Object.prototype.toString. For user-defined Function objects, the toString method returns a string containing the source text segment which was used to define the function.

JavaScript calls the toString method automatically when a Function is to be represented as a text value, e.g. when a function is concatenated with a string.

The toString() method will throw a TypeError exception ("Function.prototype.toString called on incompatible object"), if its this value object is not a Function object.

Function.prototype.toString.call('foo'); // TypeError

If the toString() method is called on built-in function objects or a function created by Function.prototype.bind, toString() returns a native function string which looks like

"function () {\n    [native code]\n}"

If the toString() method is called on a function created by the Function constructor, toString() returns the source code of a synthesized function declaration named "anonymous" using the provided parameters and function body.

It's also possible to explicitly get the string representation of a function using the + operator:

function foo() { return 'bar' }
console.log(foo + ''); // "function foo() { return 'bar' }"

Examples

Comparing actual source code and toString results

Function	Function.prototype.toString result
function f(){}	"function f(){}"
class A { a(){} }	"class A { a(){} }"
function* g(){}	"function* g(){}"
a => a	"a => a"
({ a(){} }.a)	"a(){}"
({ *a(){} }.a)	"*a(){}"
({ [0](){} }[0])	"[0](){}"
Object.getOwnPropertyDescriptor({ get a(){} }, "a").get	"get a(){}"
Object.getOwnPropertyDescriptor({ set a(x){} }, "a").set	"set a(x){}"
Function.prototype.toString	"function toString() { [native code] }"
(function f(){}.bind(0))	"function () { [native code] }"
Function("a", "b")	"function anonymous(a\n) {\nb\n}"

Specifications

Specification
ECMAScript (ECMA-262)The definition of 'Function.prototype.toString' in that specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`toString`	Chrome Full support 1	Edge Full support 12	Firefox Full support 1	IE Full support 5	Opera Full support 3	Safari Full support 1	WebView Android Full support 1	Chrome Android Full support 18	Firefox Android Full support 4	Opera Android Full support 10.1	Safari iOS Full support 1	Samsung Internet Android Full support 1.0	nodejs Full support Yes
Implements `Function.prototype.toString` revision	Chrome No support No	Edge No support No	Firefox Full support 54	IE No support No	Opera No support No	Safari No support No	WebView Android No support No	Chrome Android No support No	Firefox Android Full support 54	Opera Android No support No	Safari iOS No support No	Samsung Internet Android No support No	nodejs No support No

Legend

Full support: Full support
No support: No support