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call() and apply() in JavaScript

Published Dec 10 2018


call() and apply() are two functions that JavaScript offers to perform a very specific task: call a function and set its this value.

Check out my “this” guide to know all the details about this particular variable

A function can use the this value for many different use cases. The problem is that it’s given by the environment and cannot be changed from the outside, except when using call() or apply().

When using those methods, you can pass in an additional object that will be used as this in the function invoked.

Those functions perform the same thing, but have a difference. In call() you can pass the function parameters as a comma separated list of parameters, taking as many parameters as you need, while in apply() you pass a single array that contains the parameters:

const car = {
  brand: 'Ford',
  model: 'Fiesta'

const drive = function(from, to, kms) {
  console.log(`Driving for ${kms} kilometers from ${from} to ${to} with my car, a ${this.brand} ${this.model}`)

drive.call(car, 'Milan', 'Rome', 568)
drive.apply(car, ['Milan', 'Rome', 568])

Note that when using arrow functions this is not bound, so this method only works with regular functions.

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