observable.array excess triggers?

[alexandroppolus]

Hi!

mobx@6.1.6

const arr = observable.array([0, 0])

autorun(() => {
  console.log('arr[0] === ' + arr[0])
})
// print "arr[0] === 0"

runInAction(() => {
  arr[1] = 1
})
// print "arr[0] === 0" WTF???

autorun observes to arr[0]. Why it triggers on change arr[1]?

If using observable.object({ 0: 0, 1: 0 }), all good, autorun not triggers.

With regards,
Alex

[mweststrate]

This works as intended, arrays themselves are considered a single atom. This is an optimization decision that makes cases like this slower, but scenarios like looping or shifting items much faster. If per-key subscriptions are important, use maps insteads.

…

On Wed, Feb 17, 2021 at 8:58 AM Alexandroppolus ***@***.***> wrote: Hi! ***@***.*** const arr = observable.array([0, 0]) autorun(() => { console.log('arr[0] === ' + arr[0])})// print "arr[0] === 0" runInAction(() => { arr[1] = 1})// print "arr[0] === 0" WTF??? autorun observes to arr[0]. Why it triggers on change arr[1]? If using observable.object({ 0: 0, 1: 0 }), all good, autorun not triggers. With regards, Alex — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#2811>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAN4NBA42HPEGMY7WBNVN4DS7OAKLANCNFSM4XX6PKXQ> .

[alexandroppolus]

Ok, thanks.

I also noticed similar behavior in observable.set. This are also a single atom?

[mweststrate]

correct

…

On Wed, Feb 17, 2021 at 10:16 AM Alexandroppolus ***@***.***> wrote: Ok, thanks. I also noticed similar behavior in observable.set. This are also a single atom? — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#2811 (reply in thread)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAN4NBERUC26LG6ZGQI4NA3S7OJORANCNFSM4XX6PKXQ> .

[iChenLei]

The difference between three case.

use observable.array

This works as intended, arrays themselves are considered a single atom.
--weststrate

use observable.object

use observable.map

summary

When you use observable.array, the autorun track array itself, so whatever you do for array, the autorun will be fire.
observable.object or observable.map will create a ObservableValue for Set item or Object property , autorun only track the special variable's change. More detail is in the mobx source code.