Vue & Typescript: How to avoid TS error when accessing child component's methods

Question

I've created a custom class-based vue component and I'm trying to access its methods and/or computed properties from a parent component. There is an example in the Vue Docs that explains what I'm trying to do (https://v2.vuejs.org/v2/guide/components-edge-cases.html#Accessing-Child-Component-Instances-amp-Child-Elements). So basically it's this

class ParentComponent extends Vue {
    someMethod() {
        (this.$refs.myChildRef as ChildComponent).focus()
    }
}

class ChildComponent extends Vue {
    focus() {
        // do something
    }
}

Now, this leads to a TS error: "TS2339: Property 'focus' does not exist on type 'Vue'"

So apparently, typescript doesn't see that my ChildComponent has additional methods.

The code still works during runtime though, so it just appears to be a typescript issue.

Does anyone have an idea how to solve this?

Answer 1

Option 1: Ignore it

//@ts-ignore

Option 2: Type any

const child: any = this.$refs.myChildRef;
child.focus();

Option 3: Interface, as mentioned by @LLai

interface ComponentInterface {
    focus: () => void
}

Option 4: Merge types

As a one liner as @LaLai says

(this.$refs.myChildRef as ChildComponent & { focus: () => void }).focus()

or if you need it more often

Class ParentComponent extends Vue {
    $refs: Vue["$refs"] & {
      myChildRef: { focus: () => void }
    };  
}

Option 5: @Ref() decorator from vue-property-decorator

Class ParentComponent extends Vue {
  @Ref()
  childComponent: ChildComponent
}

Answer 2

One solution is to implement an interface on your child component.

interface ComponentInterface {
    focus: () => void
}

class ChildComponent extends Vue implements ComponentInterface {
    focus () {
        // do something
    }
}

Another option is to merge the types

class ParentComponent extends Vue {
    someMethod() {
        (this.$refs.myChildRef as ChildComponent & { focus: () => void }).focus()
    }
}

But this can get repetitive if you are calling focus a lot outside of the child component. I prefer option 1.

Answer 3

We have similar issues with our components which were built using typescript. The solution we are using for now, is just adding a ts-ignore comment before each of issue. It's not the best way but it works.

//@ts-ignore

try it out