Properties of Mobx actions.

out.txt

Increment without transaction
before incrementCounter cnt=0
after incrementCounter cnt=1
reaction computed=1
reaction cnt=1
Two increments with transaction
before incrementCounter cnt=1
after incrementCounter cnt=2
Current immediate value in transaction cnt=2
before incrementCounter cnt=2
after incrementCounter cnt=3
reaction computed=3
reaction cnt=3

test.ts

import { action, computed, observable, reaction, runInAction } from 'mobx'

class Store {
  @observable cnt: number = 0

  @computed get counter() {
    return this.cnt
  }

  @action incrementCounter() {
    console.log(`before incrementCounter cnt=${this.cnt}`)
    this.cnt++
    console.log(`after incrementCounter cnt=${this.cnt}`)
  }
}

const store = new Store()

reaction(
  () => store.cnt,
  (cnt) => {
    console.log(`reaction cnt=${cnt}`)
  },
)
reaction(
  () => store.counter,
  (cnt) => {
    console.log(`reaction computed=${cnt}`)
  },
)

console.log(`Increment without transaction`)
store.incrementCounter()
console.log(`Two increments with transaction`)
runInAction(() => {
  store.incrementCounter()
  console.log(`Current immediate value in transaction cnt=${store.counter}`)
  store.incrementCounter()
})