DEV Community

What are closures?

wrongbyte on September 29, 2022

The concept of closure is important when it comes to understanding how languages such as Javascript work - and how scopes, lifetimes and references...

Read full post

ovo7 • Sep 30 '22 • Edited

Something to add: you can create new scopes anywhere you want, provided the compiler doesn't think you're trying to initialize an object. A function body isn't necessary.


const x = 'foo'
console.log(x) // 'foo'

{
  const x = 'bar'
  console.log(x) // 'bar'
}

console.log(x) // 'foo'

Though, doing that looks ugly and probably isn't ideal. An example of a valid use case is switch statements, it allows you to isolate each case into its own local scope.

wrongbyte • Oct 1 '22

You are right, this is also something interesting about scopes. Thanks for pointing out!

Mahmoud 🦀 • Sep 30 '22 • Edited

In ReactJS, my first encounter with closures was in form of arrow functions:

I was so confused at first, then i was like: wait a sec, it is just something that returns something that in return returns something. Aha! Know what i am sayin'?

Edit: For the sake of correctness, I think this statement is somewhat wrong: