What is bind

Method of function instances creates a new function that, when called, calls this function with its this keyword set to the provided value.

Used when you want to ensure that a function always runs with a particular context (this) and arguments (known as currying).

const module = {
  x: 42,
  getX: function () {
    return this.x;
  },
};

// The function gets invoked at the global scope
const beforeBindGetX = module.getX; // undefined

// bind changes `this` reference to `module`
const afterBindGetX = beforeBindGetX.bind(module);
console.log(afterBindGetX()); // 42

Currying

function multiply(a, b) {
  return a * b;
}

const double = multiply.bind(null, 2);

console.log(double(5)); // Output: 10

In above example, null (the first argument) is the name of the object the bind would attach to.

The second argument 2 is considered the first argument.

Any subsequent argument (e.g. 5) would be additional argument to the found function.

• e.g. 5 would be passed to double function as a third argument, which becomes b parameter in multiply function definition.

Function Borrowing

bind() allows you to borrow the greet method from the person object and bind it to a different context (anotherPerson).

const person = {
  name: 'John',
  greet() {
    console.log(`Hello, ${this.name}`);
  }
};

const anotherPerson = { name: 'Jane' };

// Borrowing greet method from person object and binding it to anotherPerson
const greetJane = person.greet.bind(anotherPerson);
greetJane(); // Output: "Hello, Jane"