Strongly typing props of vue components using composition api and typescript typing system

Troy Kessier's answer is not entirely accurate. I quote the documentation on definecomponent:

Alternatively if your component does not use any option other than setup itself, you can pass the function directly […]

So there are not two ways of declaring properties, but rather two ways of declaring a component, and each of them provides its own way of typing props.

With the classic way and TypeScript, use PropType:

import { defineComponent, PropType } from 'vue'export default defineComponent({  props: {    someOptionalString: String,    someRequiredString: {      type: String,      required: true    },    someObject: {      type: Object as PropType<MyObjectType>,      required: true    },  },  // …})

Notice: PropType helps to give a correct TypeScript type to the props parameter in the setup function. But the underlying Vue type for the props remains Object and there is currently no way to enforce a better typing for these props passed by the parent component.

As explained in the official docs you can type props in two ways:

Define arops via argument annotation

import { defineComponent } from 'vue'export default defineComponent((props: { foo: string }) => {  props.foo})

Or like this

import { defineComponent } from 'vue'export default defineComponent({  props: {    foo: String  },  setup(props) {    props.foo // <- type: string  }})