Typed Component Props

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Interface

We can define the types for props through a TypeScript interface. In this case through a Typescript generic type argument.

<script setup lang="ts">
interface Props {
  tags: string[];
}
const props = defineProps<Props>();
</script>

This interface must be in the same file.

We can also skip the interface and declare types straight in the defineProps method:

<script setup lang="ts">
const props = defineProps<{
  tags: string[];
}>();
</script>

Default values

Using the method above, we loose the ability to define default values. We can bring that functionality back in with the withDefaults() method.

<script setup lang="ts">
export interface Props {
  msg?: string
  labels?: string[]
}
 
const props = withDefaults(defineProps<Props>(), {
  msg: 'hello',
  labels: () => ['one', 'two']
})
<script>

Arrays and Object require arrow syntax

You see it in the example above. When specifying an array or object as a default value, it needs to be written in arrow syntax. I forget this so often and it always throws a type error.