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Vue计算属性Computed

news 2025/7/1 0:21:32

30. Vue计算属性Computed

1. 定义

Computed属性是Vue中的一个计算属性，是一种基于其它属性值计算而来的属性值，具有缓存机制，在依赖的属性值发生变化时会重新计算。

使用computed属性可以避免在模板中书写过多的计算逻辑，提高代码可读性和维护性。

下面是一个计算属性的示例：

<template><div><h3>单价： ￥{{ price }}</h3><input type="text" v-model="count" placeholder="请输入数量">个<h3>总价： ￥{{ totalPrice }}</h3></div>
</template>
<!-- vue2 -->
<script>
export default {data() {return {price: 12,count: null}},computed: {totalPrice() {return this.price * this.count}}
}
</script>
<!-- vue3 -->
<script setup>
import { ref, computed } from "vue"
const price = ref(12)
const count = ref(0)
const totalPrice = computed(() => {return price.value * count.value
})
</script>

2. computed和methods对比

计算属性是有缓存的, 当我们多次使用计算属性时, 计算属性中的运算只会执行一次。如下图：

<template><div><div>{{ fullName }}</div><div>{{ fullName }}</div><div>{{ fullName }}</div><div>{{ fullName }}</div><div>{{ fullName }}</div><div>{{ fullName }}</div><div>{{ getFullName() }}</div><div>{{ getFullName() }}</div><div>{{ getFullName() }}</div><div>{{ getFullName() }}</div><div>{{ getFullName() }}</div></div>
</template>
<!-- vue2 -->
<script>
export default {data() {return {firstName: "Jack",lastName: "Ma"}},computed: {fullName() {console.log("computed获取fullname");return this.firstName + this.lastName;}},methods:{getFullName() {console.log("methods获取fullname");return this.firstName * this.lastName;}}
}
</script>
<!-- vue3 -->
<script setup>
import { ref, computed } from "vue"const firstName = ref("J.K.")
const lastName = ref("Rowling")const fullName = computed(() => {console.log("computed获取full");return firstName.value + lastName.value
})const getFullName = function() {console.log("methods获取full");return firstName.value + lastName.value
}
</script>

computed缓存

3. Getter和Setter

计算属性默认是只读的，也就是只用到getter。当你尝试修改一个计算属性时，你会收到一个运行时警告。只在某些特殊场景中你可能才需要用到“可写”的属性，你可以通过同时提供 getter 和 setter 来创建：

<!-- vue2 -->
<script>
export default {data() {return {firstName: "Jack",lastName: "Ma"}},computed: {fullName: {// getterget() {return this.firstName + this.lastName;},// setterset(newValue) {// 注意：我们这里使用的是解构赋值语法[this.firstName, this.lastName] = newValue.split(' ')}}},  methods:{setNewName(){//设置值触发setterthis.fullName = "Tom Mao"console.log(this.firstName, this.lastName);}}
}
</script>
<!-- vue3 -->
<script setup>
import { ref, computed } from "vue"const firstName = ref("J.K.")
const lastName = ref("Rowling")const fullName = computed({get() {return firstName.value + lastName.value},set(newValue) {[firstName.value, lastName.value] = newValue.split(' ')}
})const setNewName = function() {fullName.value = "John Doe"
}
</script>