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Drafts

One of the key and most opionionated feature of superstate is the built-in draft management. Drafts are preliminatory versions of your state that you are free to mutate without impacting the final user.

To illustrate the concept of drafts to you: when you're typing a text message to someone, the said text is just a draft as long as you don't submit it. While the text is just a draft, you're free to change it as much as you like.

Creating a draft

To create a draft, call the .sketch() method:

const count = superstate(0)

count.sketch(5)

The .sketch() method will assign 5 to the draft of count.

Updating an existing draft

const count = superstate(0)

count.sketch(5) // draft is 5
count.sketch(prev => prev + 5) // draft is 10
warning

Always prefer to .discard() a draft when you no longer want it instead of .sketch(undefined) because .discard() does more than just set the draft's value to undefined.

However, for whatever reason, if you literally just want the .draft() to become undefined, feel free to .sketch(undefined).

Reading a draft

To display the draft version of a superstate, you simply have to call .draft():

const count = superstate(0)

count.sketch(20)

console.log(count.draft()) // logs 20

Publishing a draft

When you change the value of a draft (by calling .sketch(5), for example), this change is intentionally not propagated to .now() and only exists in .draft(). In order to publish it, guess what, you gotta call .publish():

const count = superstate(0)

count.sketch(20)
count.publish()

Or, if you want a shorter version, chaining is available:

const count = superstate(0)

count.sketch(20).publish()

After you call .publish(), superstate does a few things:

  1. Assigns the value of the draft to now,
  2. disposes the value of .draft(), making it become undefined,
  3. broadcasts the change to all the subscribers. (See Broadcasting)

If you want to skip the broadcast part, just pass { silent: true } to publish:

const count = superstate(0)

count.sketch(20).publish({ silent: true })

Discarding a draft

Let's say you made changes to your draft but in the end you changed your mind. Super fineโ€”discarding drafts is simple:

const count = superstate(0)

count.sketch(10)
count.discard() // Nah, 10 is not enough!

count.sketch(20)
count.publish() // Yeah, 20 it is!

When discarding, changes will be broadcasted unless you pass true to the silent option:

const count = superstate(0)

count.sktech(10).discard({ silent: true })
info

If you discard an undefined draft, nothing will happen.

Monitoring draft changes

If you like to do something whenever a draft changes, you can subscribe to your state's draft by passing 'draft' as the second argument of the .subscribe() function:

const count = superstate(0)

count.subscribe(value => {
console.log(value)
}, 'draft') // <--- here!
info

By default, .subscribe() will only listen to .now() changes.

If you no longer want to listen to draft changes:

const count = superstate(0)
const unsubscribe = count.subscribe(console.log, 'draft')

unsubscribe()

// Now, you can safely mutate the draft that
// no changes will be broadcasted.

What changes are broadcasted?

Changes are only broadcasted if the new value of the draft is different from the previous value. With that in mind:

  • Whenever .sketch(value) is called,
  • and/or whenever .publish() is called,
  • and/or whenever .discard() is called.
info

No matter how complex the value of draft() is, superstate will deep compare the previous value with the next value, to make sure changes are only broadcasted when needed.

If you don't want changes to be broadcasted at all, most of the mutation functions allow you to pass the { silent: true } option:

const count = superstate(0)

count.sketch(5, { silent: true })
count.discard({ silent: true })
count.publish({ silent: true })

undefined drafts

If your state doesn't have a draft version, undefined will be returned when trying to read it through .draft():

const count = superstate(0)

console.log(count.draft()) // logs `undefined`

You might be wondering why and/or when a draft is undefined. Well, the idea is that superstate aims to be as respectful as possible with your user's memory usage. In short, superstate only issues drafts when needed and disposes them when no longer needed.

Draft disposal

.draft() will return undefined when:

  • You haven't .sketch() anything,
  • after you call .discard() or
  • after you call .publish().