Mastering JavaScript’s apply Method: Clever Real-Time Use Cases You Need to Know

The apply method call the method immediately with the context provided and arguments as array

Consider the below example

function getGreetings(greet1, greet2) {
  return greet1 + ' ' + this.firstName + ' ' + this.lastName + ' ' + greet2;
}

const user = { firstName: 'Vinodh', lastName: 'Thangavel' };
const user1 = { firstName: 'Prasanth', lastName: 'Rajendran' };

console.log(getGreetings.apply(user,['Welcome',':)']))
// Welcome Vinodh Thangavel :)
console.log(getGreetings.apply(user1,['Hello',':D']))
// Hello Prasanth Rajendran :D

We have a function and return value is framed with the arguments and this value

Normal function can be called with arguments, whereas when using apply method, we will be able to pass thisValue and arguments as array

Syntax

functionName.apply(thisValue, arguments[]);

As you see in the example, the same function provides different values based on change of thisValue (user1 and user2) and arguments

Whatever we pass as a first argument, that will become the this value inside that function at that point of time.

The second argument would be an array, but getGreetings expecting as individual comma separated arguments, not array,

Apply method converts the array to individual arguments, this is a very useful feature.