Discussion on: What's wrong with this code?

[JavaScript Joel]

The reason to use const instead of let is because you want your code to be immutable. (just a note, const doesn't make object immutable, you have to freeze).

So how do you eat your groceries while being immutable?

Try to view immutable code as code with the added dimension of TIME!

// the past
const { flour, eggs, turkey } = groceries

// the present
const cookedEggs = cookEggs(eggs)

// the future
const cookTurkey = turkey => ({ ...turkey, cooked: true })

At any moment in our application we can go back and look at what the state was before.

So imagine at 12:00 you had raw turkey. then at 12:30 you had cooked turkey. This is how immutable code works.

With mutable code, you know you have cooked turkey, but your past is invisible to you. You can never look at a previous state.

[Sung M. Kim]

Thanks joelnet for following up with technical aspect of the code and the implication of using const.

[Kushan Joshi]

const is a good practice, but you even continue using let with immutable code. Sometimes it’s easier and more readable to use let for an immutable object, to which you are going to apply transforms.

[JavaScript Joel]

sure.

i just try my best to make everything immutable and handle mutable state separately, like in a redux store.

[Adarsh]

@joelnet I still don't need cookTurkey instead I can do turkey.cooked = true and so it doesn't matter whether I use const or let if my code is written keeping immutability in mind.

[JavaScript Joel]

that is kind of why I mentioned '(just a note, const doesn't make object immutable, you have to freeze)' was to distinguish between const and immutable.

If you want a primitive value to be immutable, const is enough. If you want an object to be immutable, you have to freeze it as well.

So if we can assume groceries is immutable (which is should be).

const deepFreeze = require('deep-freeze')

const grocieries = deepFreeze({
  flour: {
    cooked: false
  },
  turkey: {
    cooked: false
  },
  eggs: {
    cooked: false
  }
})

Then your groceries will truly be immutable

const { turkey } = grocieries
turkey.cooked = true
//=> turkey({ cooked: false })

[Adarsh]

Sorry. Misunderstood as the freeze wasn't mentioned in the previous code. Thanks for clearing it up! :)