How to use props in in vue3

To use props with <script setup> you need to call defineProps() with the component prop options as the argument, this defines the props on the component instance and returns a reactive object with the props which you can use as follows:

<template>
  <TopNavbar title="room" />
  <div>
    {{ no }}
  </div>
</template>

<script setup>
import TopNavbar from "@/layout/TopNavbar.vue";
import { defineProps, reactive } from "vue";

const props = defineProps({
  no: String,
});

const { no } = toRefs(props);

const state = reactive({
  room: {},
});

const init = async () => {
  const { data } = await getRoomByNo(no.value);
  console.log(data);
};

init();
</script>

If you are using typescript the alternative way to do this is pass a type only declaration and infer the prop types from that. Pro’s are that you’ll get stricter type safety but you cannot have default values.

<template>
  <TopNavbar title="room" />
  <div>
    {{ no }}
  </div>
</template>

<script setup>
import TopNavbar from "@/layout/TopNavbar.vue";
import { defineProps, reactive } from "vue";

const props = defineProps<{
  no: string,
}>();

const { no } = toRefs(props);

const state = reactive({
  room: {},
});

const init = async () => {
  const { data } = await getRoomByNo(no.value);
  console.log(data);
};

init();
</script>

EDIT

Defaults with type only props are now possible:

interface Props {
  msg?: string
}

const props = withDefaults(defineProps<Props>(), {
  msg: 'hello'
})