Vue3.0初体验（Composition API）

前端开发
2020年09月10日
2993

项目环境

  • @vue-cli：4.5.4
  • node: 14.8.0

安装

当前版本的vue-cli已经支持vue3.0的preview版本，所以我们可以直接通过以下代码进行安装，在选择版本时选中vue3.0（preview）即可。

shell
vue create [project-name]

setup

To start working with the Compsition API we first need a place where we can actually use it. In a Vue component, we call this place the setup.

js
export default {
  // (e.g. setup (props, { attrs, slots, emit }))
  setup (props, context) {
    console.log(props);
    console.log(context); // 在setup()中，无法访问到this.
  }
}

composition API

reactive()

reactive()用于创建一个响应式的引用值.

vue
<template>
<!-- vue3.0 内置Fragment -->
<h1>{{ title }}</h1>
<div>
 {{ message }}
</div>
</template>

<script>
export default {
  setup () {
    const state = reactive({
      title: "reactive() 用于声明一个响应式的对象",
      message: "Hello Reactive.",
    });
    
    return state;
  }
}
</script>

ref()

ref()用于声明一个响应式的原始值，它返回一个对象，该对象只有一个value属性。(e.g. const one = ref(1); // => { value: 1 })

我们可以通过isRef()来判断某个值是否为一个ref。

vue
<template>
  <div class="page-container">
    <h2>{{ title }}</h2>
    <div class="message">{{ message }}</div>
  </div>
</template>

<script lang="ts">
import { 
  defineComponent, 
  isRef,
  onMounted, 
  ref,
} from 'vue';

export default defineComponent({
  name: 'Ref',
  setup () {
    const title = ref('ref() 用于声明单一的原始值'),
          message = ref('Hello ref.');

    let nonRef= 'non-ref';

    onMounted(() => {
      setTimeout(() => {
        message.value = title.value; // 组件挂载完3s后 将message的值变成title的值

        console.log('title is ref? ', isRef(title))
        console.log('nonRef is ref? ', isRef(nonRef))
      }, 3000)
    })
    
    return {
      title,
      message
    }
  }
});
</script>

computed()

vue3.0提供的computed()，它可以接受一个回调函数作为参数，也可以接受一个包含了getter、setter的对象作为参数;

vue
<template>
  <div class="page-container">
    <h2>Computed</h2>
    <div class="message">
      FirstName: {{ firstName }}
      <br />
      LastName: {{ lastName }}
      <br />
      FullName: {{ fullName }}
    </div>
    <button @click="changeName(fullName === 'Wu Wang' ? 'San Zhang' : 'Wu Wang')">ChangeName</button>
  </div>
</template>

<script lang="ts">
import { computed, defineComponent, isRef, ref } from 'vue';

export default defineComponent({
  name: 'Computed',

  setup () {
    let firstName = ref('San'),
        lastName = ref('Zhang');

    // 当参数为一个函数时，返回一个只读的ref值
    const zero = computed(
      () => 0
    )
    console.log(isRef(zero));

    // 当参数为一个含有 getter 和 setter 函数的对象时，
    // computed 返回一个可读写的ref值
    const fullName = computed({
      get () {
        return firstName.value + ' ' + lastName.value;
      },

      set (name: string) {
        let [first, last] = name.split(' ');

        firstName.value = first;
        lastName.value = last;
      }
    });

    const changeName = function (name: string) {
      fullName.value = name;
    }

    return {
      firstName,
      lastName,
      fullName,
      changeName
    }
  }
});
</script>

watch()

通过watch()，我们可以很轻易地监听某个值的变化。

watch.vue

vue
<template>
  <div class="page-container">
    <h2>Watch</h2>
    <p>
      <input type="text" v-model="keyword" />
    </p>
    <div class="message">
      {{ message }}
    </div>
  </div>

  <watch-on-cleanup />
</template>

<script lang="ts">
import { defineComponent, ref, watch } from 'vue';

import WatchOnCleanup from '@/components/Main/WatchOnCleanup.vue';

export default defineComponent({
  name: 'Watch',
  components: {
    WatchOnCleanup
  },
  setup () {
    const keyword = ref(''),
          message = ref('输入1秒之后将结果显示.'),
          loading = ref(false);
          
    const stop = watch(
      keyword,
      (keyword, prevKeyword) => {
        setTimeout(() => {
          if (keyword === '') {
            message.value = '输入1秒之后将结果显示.'
          } else {
            message.value = keyword
          }
        }, 1000)
      }
    );

    return {
      keyword,
      message
    }
  }
});
</script>

components/Main/WatchOnCleanup.vue

vue
<template>
  <div class="page-container">
    <h2>Watch onCleanup</h2>
    <p>
      <input type="text" v-model="keyword" />
    </p>
    <div class="message">
      {{ message }}
    </div>
  </div>
</template>

<script lang="ts">
import {
  defineComponent, ref, watch
} from 'vue';

export default defineComponent({
  name: 'WatchOnCleanup',

  setup () {
    const keyword = ref(''),
          message = ref('onCleanup 实现 防抖功能');

    const asyncFunc = (val: string) => {
      return setTimeout(() => {
        message.value = val;
      }, 1000);
    } 

    const stop = watch(
      keyword,
      (keyword, prev, onCleanup) => {
        const t = asyncFunc(keyword);

        // onCleanup 如果watch监听被重复执行了，则会先清除上一次未完成的异步任务
        onCleanup(() => clearTimeout(t));
      }
    );

    // stop(); // 可以通过执行watch的返回值来结束监听动作

    return {
      keyword,
      message
    }
  }
})
</script>

LifeCycle

在vue3.0中，提供了与以往版本稍有不同的生命周期钩子

  • beforeCreate() -> setup()
  • created() -> setup()
  • beforeMount() -> onBeforeMount()
  • mounted() -> onMounted()
  • beforeUpdate() -> onBeforeUpdate()
  • updated() -> onUpdated()
  • beforeDestroy() -> onBeforeUnmount()
  • destroyed() -> onUnmouted()
  • errorCaptured() -> onErrorCaptured()

当然，vue3.0是兼容2.x版本的，所以之前的那些生命周期钩子也是可以使用的。

vue
<template>
  <div class="page-container">
    <h2>{{ title }}</h2>
    <ul class="list">
      <li
        class="item"
        v-for="(item, index) of list"
        :key="index"
      >
        <span class="old">{{ item[0] }}</span>
        <span class="divider">-></span>
        <span class="new">{{ item[1] }}</span>
      </li>
    </ul>
  </div>
</template>

<script lang="ts">
import { app, el } from '@/main';
import {
  defineComponent,
  reactive,
  ref,
  onBeforeMount,
  onMounted,
  onBeforeUpdate,
  onUpdated,
  onBeforeUnmount,
  onUnmounted,
  onErrorCaptured,
} from 'vue';

export default defineComponent({
  name: 'LifeCycle',

  setup (props, context) {
    const list = reactive([
      ['2.x', '3.0'],
      ['beforeCreate()', 'setup()'],
      ['created()', 'setup()'],
      ['beforeMount()', 'onBeforeMount()'],
      ['mounted()', 'onMounted()'],
      ['beforeUpdate()', 'onBeforeUpdate()'],
      ['updated()', 'onUpdated()'],
      ['beforeDestroy()', 'onBeforeUnmount()'],
      ['destroyed()', 'onUnmouted()'],
      ['errorCaptured()', 'onErrorCaptured()']
    ]);

    let title = ref('LifeCycle');

    console.log('setup called.');

    onBeforeMount(() => {
      console.log('onBeforeMount');
    });

    onMounted(() => {
      console.log('onMounted');

      setTimeout(() => {
        title.value = title.value + ' has changed.';
      }, 3000);
    });

    onBeforeUpdate(() => {
      console.log('onBeforeUpdate');
    });

    onUpdated(() => {
      console.log('onUpdated');

      setTimeout(() => {
        app.unmount(el); // 1s后卸载应用 
      }, 1000)
    });

    onBeforeUnmount(() => {
      console.log('onBeforeUnmount');
    })

    onUnmounted(() => {
      console.log('onUnmount');
    });

    return {
      list,
      title
    }
  },

  beforeCreate () {
    console.log('beforeCreate')
  },

  created () {
    console.log('created')
  },

  beforeMount () {
    console.log('beforeMount')
  },

  mounted () {
    console.log('mounted')
  },

  beforeUpdate () {
    console.log('beforeUpdate')
  },

  updated () {
    console.log('updated');
  },

  beforeDestroy () {
    console.log('beforeDestroy')
  },

  destroyed () {
    console.log('destroyed')
  },

  errorCaptured () {
    console.log('errorCaptured')
  }
});
</script>

output:

plain-text
setup called.
beforeCreate
created
onBeforeMount
beforeMount
onMounted
mounted
onBeforeUpdate
beforeUpdate
onUpdated
updated
onBeforeUnmount
onUnmount

Provide() And Inject()

强大的provide()与inject()，意味着我们可以用来替代某些需要使用vuex来完成工作的场景。

父组件provide()提供的值，在其任意的子孙组件中都可以通过inject()来获取。

父组件：

vue
<template>
  <div class="page-container">
    <comp-header></comp-header>
    <comp-content></comp-content>
  </div>
</template>

<script lang="ts">
import {
  defineComponent,
  provide
} from 'vue';

import CompHeader from '@/components/Main/ProvideAndInject/Header/index.vue';
import CompContent from '@/components/Main/ProvideAndInject/Content/index.vue';

export default defineComponent({
  components: {
    CompHeader,
    CompContent
  },

  setup () {
    provide('globalTitle', 'Provide & Inject');
    provide('globalLogo', 'Logo.');
    provide('globalContent', 'Vue3.0中，父组件通过provide(key, value)提供的值，在其任意的子孙组件里面都可以通过inject(key)来获取。');
  }
});
</script>

components/Main/ProvideAndInject/Header/index.vue

vue
<template>
  <h2>{{ title }}</h2>
  <logo />
</template>

<script lang="ts">
import {
  inject,
  ref,
  defineComponent
} from 'vue';

import Logo from './Logo.vue';

export default defineComponent({
  name: 'CompHeader',
  components: {
    Logo
  },
  setup () {
    const title = ref(inject('globalTitle'));

    return {
      title
    }
  }
});
</script>

components/Main/ProvideAndInject/Header/Logo.vue

vue
<template>
  <div class="logo">CompHeader Sub Component&lt;{{ logo }}&gt;</div>
</template>

<script lang="ts">
import { defineComponent, inject, ref } from 'vue';

export default defineComponent({
  name: 'Logo',

  setup () {

    const logo = ref(inject('globalLogo'));

    return {
      logo
    }
  }
})
</script>

components/Main/ProvideAndInject/Content/index.vue

vue
<template>
  <div class="content">
    <p>From Views/ProvideAndInject：{{ content }}</p>
  </div>
</template>

<script lang="ts">
import { defineComponent, inject, ref } from 'vue';

export default defineComponent({
  name: 'CompContent',
  setup () {
    const content = ref(inject('globalContent'));

    return {
      content
    }
  }
})
</script>

renderFunction

vue3.0提供h()函数来替代以往的render()函数。

vue
<script lang="ts">
import { h, ref, defineComponent, onMounted } from 'vue';

export default defineComponent({
  setup () {
    const count = ref(0),
          title = ref('RenderFunction');

    onMounted(() => {
      setInterval(() => {
        count.value ++
      }, 500)
    })

    return () => {
      return h(
        'div',
        [
          h('h2', title.value),
          h('p', 'count: ' + count.value)
        ]
      )
    }
  }
})
</script>

附

【demo地址】

VueJSvue3.0
Vue中的computed与watch的区别
Markdown 语法精选