computed() และ watch()

computed() ใน Composition API

<script setup>
import { ref, computed } from 'vue';

const items = ref([{ price: 10 }, { price: 20 }, { price: 30 }]);
const tax = ref(0.1);

const subtotal = computed(() => items.value.reduce((s, i) => s + i.price, 0));
const total = computed(() => subtotal.value * (1 + tax.value));
</script>

computed() ที่เขียนค่าได้

const firstName = ref('Alice');
const lastName  = ref('Smith');

const fullName = computed({
  get: () => `${firstName.value} ${lastName.value}`,
  set: (val: string) => {
    [firstName.value, lastName.value] = val.split(' ');
  }
});

fullName.value = 'Bob Jones'; // sets both refs

พื้นฐานของ watch()

import { ref, watch } from 'vue';

const query = ref('');

watch(query, (newVal, oldVal) => {
  console.log(`Changed from '${oldVal}' to '${newVal}'`);
  searchAPI(newVal);
});

การเฝ้าดู ref เทียบกับ reactive

const count = ref(0);
watch(count, val => console.log('count:', val));

const state = reactive({ count: 0, name: '' });
watch(() => state.count, val => console.log('state.count:', val));

การเฝ้าดูแบบลึก

const user = ref({ name: 'Alice', address: { city: 'NY' } });

watch(user, (newUser) => {
  console.log('user changed:', newUser);
}, { deep: true });

การเฝ้าดูทันที

watch(userId, async (id) => {
  user.value = await fetchUser(id);
}, { immediate: true }); // runs once on setup, then on change

watchEffect()

import { watchEffect } from 'vue';

watchEffect(() => {
  // runs immediately and whenever query or page changes:
  fetchResults(query.value, page.value);
});

watchEffect เทียบกับ watch

การหยุด Watcher