JavaScript reference

Function.prototype.bind

Creates a copy of a function with a fixed this and, optionally, arguments.

Available since: ES5

Syntax

fn.bind(thisArg, ...args)

Parameters

Parameter	Type	Description
thisArg	any	The this value for the new function.
...args	any	Optional. Arguments to fix in advance.

Return value

FunctionA new function with this and arguments bound.

Examples

A method loses this when passed on its own:

class User {
  constructor(name) {
    this.name = name;
  }
 
  greet() {
    return `Hi, ${this.name}`;
  }
}
 
const anna = new User('Anna');
const lost = anna.greet;
const bound = anna.greet.bind(anna);
 
try {
  lost();
} catch (error) {
  console.log(error.name);
}
 
console.log(bound());

Output:

TypeError
Hi, Anna

Partial application — fixing the first argument:

const multiply = (a, b) => a * b;
const triple = multiply.bind(null, 3);
 
console.log(triple(5));

Output:

Notes

The most common case is passing a method to an event handler or timer. An arrow function is often used instead of bind(): () => user.greet().

In the tutorial

this, call, apply and bind — How this is determined in JavaScript, why a method loses its context, and how to set this by hand with call, apply and bind.

Thanks for reading!