Rule proposition: `no-side-effects-in-computed-properties`

This rule would check if there are no side effects inside computed properties.

So this example would throw an error:

export default {
  computed: {
    hello() {
      this.lastName = 'Dolor' // <- error "Unexpected side effect in computed property 'hello'"
      return `Hello ${this.firstName} ${this.lastName}`
    }
  },
  data() {
    return {
      firstName: 'Lorem',
      lastName: 'Ipsum'
    }
  }
}

What do you think @mysticatea @chrisvfritz ?

[LinusBorg]

Would this rule also check for things like:

export default {
  computed: {
    hello() {
      this.sideEffect() // <- error "Unexpected side effect in computed property 'hello'"
      const formattedValue = this.format(value) // <- no error
      return `Hello ${this.firstName} ${this.lastName}`
    }
  },
methods: {
  sideEffect() {
    // some side effect.
  },
  format(value) {
    return // ...
  }
}

[michalsnik]

Ready in v3.6.0 🚀 Let’s leave such edge cases for further consideration, we need to be agile and constantly improve those rules starting with simple solutions. I’m going to move those ideas to separate issue and closing this one. Thanks for a great discussion here guys!