CODEWITHSUNDEEP
typescriptvue.jsionic-frameworkeslintionic5
Dan
Dan

Reputation: 5986

How to resolve ESLint error in defining `this` inside nested scope in Ionic Vue method

I have an Ionic Vue app which uses the slides component to modify a reactive property each time it transitions. The pertinent code is like this:

<script lang="ts">
import { IonPage, IonContent, IonSlides, IonSlide,} from '@ionic/vue'

export default {
  name: 'Splash',
  components: { IonPage, IonContent, IonSlides, IonSlide,},
  data() {
    return {
      contentClass: 'bg-gradient-1',
    }
  },
  setup() {
    const slideOpts = {
      autoplay: {
        delay: 4000,
      },
    }    
    return { slideOpts }
  },
  methods: {
    slideChange({ target }) {
      const vm = this
      target.getActiveIndex().then((i) => {
        vm.contentClass = 'bg-gradient-' + i
      })
    },
  },
}
</script>

This generates the following error:

Unexpected aliasing of 'this' to local variable @typescript-eslint/no-this-alias

The reason I'm using const vm = this is because once inside the getActiveIndex method, the scope of this changes and I can't modify the contentClass data property.

Rather than just blindly disabling the ESLint rule to allow this to be assigned to a constant I wondered if anyone was able to offer a better/proper solution?

Many thanks.

Upvotes: 9

Views: 10852

Answers (4)

RBILLC
RBILLC

Reputation: 190

When using an arrow function, 'this' refers to the surrounding context. So no need to do that anymore!

element.addEventListener('click', () => {
     console.log(this); // 'this' refers to the surrounding context
});

Upvotes: 0

Aaron Saunders
Aaron Saunders

Reputation: 33345

It may also be solved by not using data and going all-in with the setup approach:

<script lang="ts">
import { IonPage, IonContent, IonSlides, IonSlide,} from '@ionic/vue'

export default {
  name: 'Splash',
  components: { IonPage, IonContent, IonSlides, IonSlide,},
  setup() {
    const contentClass = ref<any>('bg-gradient-1');
    const slideChange = ({ target }) => {
      target.getActiveIndex().then((i) => {
        contentClass.value = 'bg-gradient-' + i
      })
    },
    const slideOpts = {
      autoplay: {
        delay: 4000,
      },
    }    
    return { slideOpts, contentClass, slideChange }
  }
}
</script>

Upvotes: 3

pedro.caicedo.dev
pedro.caicedo.dev

Reputation: 2445

In .eslintrc file on rules key add "@typescript-eslint/no-this-alias": 0, for example in my case:

"rules": {
        "@typescript-eslint/no-var-requires": 0,
        "@typescript-eslint/no-explicit-any": 0,
        "@typescript-eslint/no-this-alias": 0,
        "no-console": 1, // Means warning
        "prettier/prettier": 2 // Means error
    }

Upvotes: 0

Amaarockz
Amaarockz

Reputation: 4684

yes there is one solution. You can add the following object in your ESlint config file

{
  "@typescript-eslint/no-this-alias": [
    "error",
    {
      "allowDestructuring": true, // Allow `const { props, state } = this`; false by default
      "allowedNames": ["vm"] // Allow `const vm= this`; `[]` by default
    }
  ]
}

for more info also check on TSLint: no-this-assignment

Upvotes: 9

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