Discussion on: Javascript call and apply 101

[Jannik Wempe]

Love the simplicity and especially the trick about how to remember the difference.

But I am missing the part "When to use call and when to use apply", which I was most interested in ;-) Is it just about preference?

[Jake Whelan]

It just depends on the structure of your arguments.

call is useful for manually calling a function where you have explicitly defined arguments.

const a = 'bar'
const b = 'baz'

foo.call({}, a, b)

But sometimes you have an array of arguments and you want to programmatically call a function with them, that's where apply is useful.

const args = ['bar', 'baz']

foo.apply({}, args)

That said, with the advent of the spread/rest operator (...), apply is redundant.

const args = ['bar', 'baz']

// notice this is using call, not apply!
foo.call({}, ...args)

[Igor Irianto]

Hey Jannik! I'm glad you liked it.
As for the usage, it is mostly up to your preference. In addition to what Jake covered (for arguments), you can use call and apply to give this inside a function a different object.

const someObj = {
  name: 'iggy',
  sayName() {
     console.log(`The name is ${this.name}`)
  }
}

Normally I'd do someObj.sayName(). But if one day I go back to reuse sayName, but I want to pass it a different name, you can just use call/apply. someObj.sayName.call({name: 'Russell'}).

It's like inheriting and reusing other object's properties.