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no-side-effects-in-computed-properties.md

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vue/no-side-effects-in-computed-properties
disallow side effects in computed properties
v3.6.0

vue/no-side-effects-in-computed-properties

disallow side effects in computed properties

  • ⚙️ This rule is included in all of "plugin:vue/vue3-essential", "plugin:vue/essential", "plugin:vue/vue3-strongly-recommended", "plugin:vue/strongly-recommended", "plugin:vue/vue3-recommended" and "plugin:vue/recommended".

📖 Rule Details

This rule is aimed at preventing the code which makes side effects in computed properties and functions.

It is considered a very bad practice to introduce side effects inside computed properties and functions. It makes the code not predictable and hard to understand.

<script>
/* ✓ GOOD */
export default {
  computed: {
    fullName () {
      return `${this.firstName} ${this.lastName}`
    },
    reversedArray () {
      return this.array.slice(0).reverse() // .slice makes a copy of the array, instead of mutating the orginal
    }
  }
}
</script>
<script>
/* ✗ BAD */
export default {
  computed: {
    fullName () {
      this.firstName = 'lorem' // <- side effect
      return `${this.firstName} ${this.lastName}`
    },
    reversedArray () {
      return this.array.reverse() // <- side effect - orginal array is being mutated
    }
  }
}
</script>
<script>
import {computed} from 'vue'
/* ✓ GOOD */
export default {
  setup() {
    const foo = useFoo()

    const fullName = computed(() => `${foo.firstName} ${foo.lastName}`)
    const reversedArray = computed(() => {
      return foo.array.slice(0).reverse() // .slice makes a copy of the array, instead of mutating the orginal
    })
  }
}
</script>
<script>
import {computed} from 'vue'
/* ✗ BAD */
export default {
  setup() {
    const foo = useFoo()
    
    const fullName = computed(() => {
      foo.firstName = 'lorem' // <- side effect
      return `${foo.firstName} ${foo.lastName}`
    })
    const reversedArray = computed(() => {
      return foo.array.reverse() // <- side effect - orginal array is being mutated
    })
  }
}
</script>

🔧 Options

Nothing.

📚 Further Reading

🚀 Version

This rule was introduced in eslint-plugin-vue v3.6.0

🔍 Implementation