自定义v-model

v-model实际上是语法糖：

<input type="text" v-model="test" />

// 就是相当于: 
<input type="text" 
            :value="test" 
            @input="test= $event.target.value" />

案例：

<!-- 子组件 -->
<template>
    <!-- 例如：vue 颜色选择 -->
    <input type="text"
        :value="text1"
        @input="$emit('change1', $event.target.value)"
    >
    <!--
        1. 上面的 input 使用了 :value 而不是 v-model
        2. 上面的 change1 和 model.event1 要对应起来
        3. text1 属性对应起来
    -->
</template>

<script>
export default {
    model: {
        prop: 'text1', // 对应 props text1
        event: 'change1'
    },
    props: {
        text1: String,
        default() {
            return ''
        }
    }
}
</script>

<template>
    <div>
        <p>{{name}}</p>
        <CustomVModel v-model="name"/>
    </div>
</template>

<script>
import CustomVModel from './CustomVModel'

export default {
    components: {
        CustomVModel
    },
    data() {
        return {
            name: 'yong',
        }
    }
}
</script>

$nextTick异步渲染

$nextTick会在DOM渲染之后被触发，以获取最新的DOM节点
案例：

<template>
  <div id="app">
    <ul ref="ul1">
        <li v-for="(item, index) in list" :key="index">
            {{item}}
        </li>
    </ul>
    <button @click="addItem">添加一项</button>
  </div>
</template>

<script>
export default {
  name: 'app',
  data() {
      return {
        list: ['a', 'b', 'c']
      }
  },
  methods: {
    addItem() {
        this.list.push(`${Date.now()}`)
        this.list.push(`${Date.now()}`)
        this.list.push(`${Date.now()}`)

        // 1. 异步渲染，$nextTick 待 DOM 渲染完再回调
        this.$nextTick(() => {
          // 获取最新的DOM 元素
          const ulElem = this.$refs.ul1
          // eslint-disable-next-line
          console.log( ulElem.childNodes.length )
        })
    }
  }
}
</script>

slot插槽

默认插槽

<!-- 子组件 -->
<template>
    <a :href="url">
        <slot>
            默认内容，即父组件没设置内容时，这里显示
        </slot>
    </a>
</template>

<script>
export default {
    props: ['url'],
    data() {
        return {}
    }
}
</script>

<!-- 父组件 -->
<SlotDemo :url="website.url">
      {{website.title}}    // 有值就显示值，没值就显示默认内容
</SlotDemo>

作用域插槽

获取子组件的插槽值

<!-- 子组件 -->
<template>
    <a :href="url">
        <slot :slotData="website">
            {{website.subTitle}} <!-- 默认值显示 subTitle ，即父组件不传内容时 -->
        </slot>
    </a>
</template>

<script>
export default {
    props: ['url'],
    data() {
        return {
            website: {
                url: 'http://Editor.com/',
                title: 'Editor',
                subTitle: '轻量级富文本编辑器'
            }
        }
    }
}
</script>

<!-- 父组件 -->
        <ScopedSlotDemo :url="website.url">
            <template v-slot="slotProps">
                {{slotProps.slotData.title}}     // 获取子组件中的插槽数据Editor
            </template>
        </ScopedSlotDemo>

在element-ui中使用v-slot="scope"，可以拿到scope.row当前行的数据
v-slot="scope"只能用于template和组件标签

        <el-table-column label="状态">
          <!-- 作用域插槽拿到当前行的数据 -->
          <template v-slot="scope">
            <el-switch
              v-model="scope.row.mg_state"
              active-color="#13ce66"
              inactive-color="#DCDFE6"
              @change="userStateChanged(scope.row)"
            >
            </el-switch>
          </template>
        </el-table-column>

具名插槽

多个插槽，通过命名来区分

// 子组件
<template>
  <div class="slottwo">
    <div>slottwo</div>
    <slot name="header"></slot>
    <slot></slot>
    <slot name="footer"></slot>
  </div>
</template>

<!-- 父组件 -->
<template>
  <div>
    <slot-two>
      <p>123456</p>
      <template slot="header">
          <p>我是name为header的slot</p>
      </template>
      <p slot="footer">我是name为footer的slot</p>
    </slot-two>
  </div>
</template>

image.png

异步组件

用的时候再加载，不用不加载，按需加载，异步加载大组件

<template>
    <div>
        <FormDemo v-if="showFormDemo"/>
        <button @click="showFormDemo = true">show form demo</button>
    </div>
</template>

<script>
    components: {
        FormDemo: () => import('../BaseUse/FormDemo')
    },
    data() {
        return {
            showFormDemo: false
        }
    }
</script>

keep-alive组件缓存

<template>
    <div>
        <button @click="changeState('A')">A</button>
        <button @click="changeState('B')">B</button>
        <button @click="changeState('C')">C</button>

        <keep-alive> <!-- tab 切换 -->
            <KeepAliveStageA v-if="state === 'A'"/> <!-- v-show -->
            <KeepAliveStageB v-if="state === 'B'"/>
            <KeepAliveStageC v-if="state === 'C'"/>
        </keep-alive>
    </div>
</template>

<script>
import KeepAliveStageA from './KeepAliveStateA'
import KeepAliveStageB from './KeepAliveStateB'
import KeepAliveStageC from './KeepAliveStateC'

export default {
    components: {
        KeepAliveStageA,
        KeepAliveStageB,
        KeepAliveStageC
    },
    data() {
        return {
            state: 'A'
        }
    },
    methods: {
        changeState(state) {
            this.state = state
        }
    }
}
</script>

// 其中一个组件，其他都是一样
<template>
    <p>state A</p>
</template>

<script>
export default {
    mounted() {
        // eslint-disable-next-line
        console.log('A mounted')
    },
    destroyed() {
        // eslint-disable-next-line
        console.log('A destroyed')
    }
}
</script>

如果不加<keep-alive>，则不会缓存，每次切换都有执行加载销毁

每次切换都有执行加载销毁

用keep-alive包起来实现组件缓存

        <keep-alive> <!-- tab 切换 -->
            <KeepAliveStageA v-if="state === 'A'"/> <!-- v-show -->
            <KeepAliveStageB v-if="state === 'B'"/>
            <KeepAliveStageC v-if="state === 'C'"/>
        </keep-alive>

点过后就被缓存了

如果里面有不需要缓存的：

// 将不需要缓存的名字加上去
        <keep-alive exclude="Profile,User"> 
            <router-view/>            
        </keep-alive>