call, apply & bind

call, apply and bind sometimes we called it function borrowing

Call: it can map a function with different object like-

let name = {
  firstName: 'Danish',
  lastName: 'Raza',
};

let printFullName = function () {
  console.log(this.firstName + ' ' + this.lastName);
};

let name2 = {
  firstName: 'Lav',
  lastName: 'Singhania',
};

console.log(printFullName.call(name2));

above code we can just call the function printFullName by passing the object which we want to call.

call method accept the object as a parameter which you want to call. In above case we are calling name 2 object

We can also pass the extra parameter to the call function like-

let name = {
  firstName: 'Danish',
  lastName: 'Raza',
};

let printFullName = function (hometown, state) {
  console.log(
    this.firstName + ' ' + this.lastName + ' is from ' + hometown + ', ' + state
  );
};

let name2 = {
  firstName: 'Lav',
  lastName: 'Singhania',
};

console.log(printFullName.call(name2, 'uttam nagar east', 'delhi'));

in the same example we add the two extra parameter named hometown and state. by this way we can pass infinite no of parameters to the function.

apply: bind method is same as call method except we pass extra parameters in the array form, like-

let name = {
  firstName: 'Danish',
  lastName: 'Raza',
};

let printFullName = function (hometown, state) {
  console.log(
    this.firstName + ' ' + this.lastName + ' is from ' + hometown + ', ' + state
  );
};

let name2 = {
  firstName: 'Lav',
  lastName: 'Singhania',
};

console.log(printFullName.apply(name2, ['uttam nagar east', 'delhi']));

bind: bind is bit different from these two. In bind method it returns the copy of the existing function that we can invoke later.

let name = {
  firstName: 'Danish',
  lastName: 'Raza',
};

let printFullName = function (hometown, state) {
  console.log(
    this.firstName + ' ' + this.lastName + ' is from ' + hometown + ', ' + state
  );
};

let name2 = {
  firstName: 'Lav',
  lastName: 'Singhania',
};

const printName = printFullName.bind(name2, ['uttam nagar east', 'delhi'])

// printname is the copy of printFullName function which we are invoking below.

printName();

in this code snippet printName is the exact copy of prinFullName functon.