better-vue-with-components.vue

<!-- 1. PROPS  -->

<!-- JS -->
<script setup>
import { defineProps } from 'vue';

const props = defineProps({
  foo: { type: String, required: true },
  bar: Number,
});

// props.foo is a string
// props.bar is a number or undefined
</script>


<!-- TS -->
<script setup lang="ts">
const props = defineProps<{
  foo: string;
  bar?: number;
}>()
</script>


<script setup lang="ts">
interface Props {
  foo: string;
  bar?: number;
}

const props = defineProps<Props>()
</script>



<!-- 2. EMITS  -->
<!-- JS -->
<script setup>
const emit = defineEmits(['change', 'update'])
</script>

 <!-- TS -->
 <script setup lang="ts">
const emit = defineEmits<{
  change: [id: number]
  update: [value: string]
}>()
</script>



<!-- 3. Typing Ref and Reactive Data => Inference -->
<script setup>
import { ref } from 'vue';

const count = ref(0); 
count.value = 'string';  // error, inference, we expect number
</script>


<!-- 4. Typing Server Responses -->
<script setup lang="ts">
import { ref, onMounted } from 'vue';

interface User {
  id: number;
  name: string;
  email: string;
}

const userData = ref<User | null>(null);

onMounted(async () => {
  const response = await fetch('https://api.example.com/user');
  const data: User = await response.json();
  userData.value = data; // TypeScript ensures data usages match the User interface
});
</script>


<!-- 5. Typing Computed Data -->
import { ref, computed } from 'vue'

const count = ref(0)
// inferred type: ComputedRef<number>
const double = computed(() => count.value * 2)
// => TS Error: Property 'split' does not exist on type 'number'
const result = double.value.split('')

// or explicitely define return type
const double = computed<number>(() => {
  // type error if this doesn't return a number
})



<!-- 6. Typing Scoped Slots-->
<template>
  <slot :msg="message"></slot>
</template>

<script setup lang="ts">
const message = 'Hello, Vue!';

const slots = defineSlots<{
  default: (props: { msg: string }) => any;
}>()
</script>


<!-- 7. Typing Template Refs -->
<script setup lang="ts">
import { useTemplateRef, onMounted } from 'vue';

const myInput = useTemplateRef('my-input');

onMounted(() => {
  myInput.value?.focus(); 
});
</script>

<template>
  <input ref="my-input" />
</template>



<!-- 8. Typing Provide/Inject -->
<!-- ParentComponent.vue -->
<script setup lang="ts">
import { provide } from 'vue';

const theme = 'dark';
provide('theme', theme);
</script>

<!-- ChildComponent.vue -->
<script setup lang="ts">
import { inject } from 'vue';

const theme = inject<string>('theme'); // Inject with expected type
// TypeScript ensures that 'theme' is of type string
</script>


<!-- 9. Generics -->
<script setup lang="ts" generic="T">
defineProps<{
  items: T[];      // Array of items of type T
  selected: T;     // Single selected item of type T
}>()
</script>


<!-- 10. Typed Composables -->
// useUser.ts
import { ref } from 'vue';

interface User {
  id: number;
  name: string;
  age: number;
}

export function useUser() {
  const user = ref<User | null>(null);

  function fetchUser(id: number) {
    // Fetching user logic
    user.value = { id, name: 'John Doe', age: 30 };
  }

  return { user, fetchUser };
}