? Function.prototype.bind() in JavaScript

What is bind()?

• bind() creates a new function with a fixed this context and optionally prepends arguments.

• It does not call the function immediately but returns a new function you can call later.

• Useful to lock the value of this for functions used as callbacks or event handlers.

Syntax

const boundFunc = func.bind(thisArg[, arg1[, arg2[, ...]]]);

• thisArg: The value to bind as this.

• arg1, arg2, ...: Optional arguments to prepend to the new function.

Example 1: Binding this

const person = {  name: "John",  greet() {    console.log("Hello, " + this.name);  }};const greet = person.greet;greet();  // undefined or global contextconst boundGreet = person.greet.bind(person);boundGreet();  // Hello, John

Example 2: Partial Application (Pre-filling Arguments)

function multiply(a, b) {  return a * b;}const double = multiply.bind(null, 2);console.log(double(5));  // 10console.log(double(10)); // 20

Key Points

• bind() returns a new function.

• It does not invoke the original function immediately.

• It fixes the this context for the new function.

• You can also fix some initial arguments (partial application).

Difference Between bind(), call(), and apply()

Summary Table

Want to see how bind() is used in event handlers or how to create your own bind function polyfill?