Solution to the flickering problem of vue page loading

This article mainly introduces the solution to the flashing problem of vue page loading. The article mentions the difference between v-if and v-show, and two methods to solve the problem of {{message}} crashing when the vue page is loading. For those who are interested, let’s take a look.

The difference between v-if and v-show

v-if will only work when the conditions are met It will be compiled only when the condition is met, while v-show will always compile regardless of whether the conditions are met. The display and hiding of v-show is just a simple switch of the display attribute of CSS.

In other words, when using v-if, if the value is false, then the page will not have this html tag generated. And v-show: regardless of whether its value is false or true, the html element will exist, just simply switch the display attribute of the css.

Usage scenarios

Generally speaking, v-if has a higher switching cost and v-show has a higher initial rendering cost . Therefore, v-show is better if you need to switch frequently, and v-if is better if conditions are unlikely to change at runtime.

In addition

1. The v-if directive can be applied to the template packaging element, but v-show does not support template

2. When applying v-show to a component, there will be a problem because of the priority of the instruction v-else. The solution is to replace v-else with another v-show

 // 错误
  <custom-component v-show="condition"></custom-component>
  <p v-else>这可能也是一个组件</p>
     // 正确做法
  <custom-component v-show="condition"></custom-component>
  <p v-show="!condition">这可能也是一个组件</p>

Solution to {{message}} crash when vue page is loading

Method one: v- cloak

When the v-cloak directive is used with css rules such as [v-cloak]{display:none}, this directive can hide uncompiled Mustache tags until the instance is ready.
The v-cloak directive can bind a set of css styles like a css selector, and then this set of css will take effect until the instance is compiled.

  eg:
    // <p> 不会显示，直到编译结束。
    [v-cloak]{
      display:none;
        }
    <p v-cloak>
       {{ message }}
    </p>

Method 2: v-text

In vue we will wrap the data in two curly brackets , and then put it into HTML, but inside vue, all double brackets will be compiled into a v-text directive of textNode.

The advantage of using v-text is always better performance, and more importantly, it can avoid FOUC (Flash of Uncompiled Content), which is the problem encountered above.

eg:
  <span v-text="message"></span>
  <!-- same as -->
  <span>{{message}}</span>

Supplement:

vue page loading progress bar component

I first saw the page loading progress bar on YouTube, and later it can be seen on almost all major websites, so that users will not face a completely blank space when loading the page. The page is in a daze to improve the user experience

But from a development perspective, it is really difficult to grasp the authenticity of this kind of progress bar, because we cannot count the progress before the logic code is loaded, and the logic code It is also impossible to count your own progress. In addition, it is impossible for us to monitor the loading of all resources.

In fact, users don’t care what percentage of your page is loaded, but what they really care about is how long it is until it is fully loaded, and whether the blank page has not been fully loaded or is blank after it is loaded. of. So we don't need to "simulate" a progress bar, use a fake animation effect to simulate loading before the back-end data is returned, and read the progress bar and hide it after the data is returned.

// progress-bar.vue
<template>
 <transition name="fade">
  <p class="progress-bar" v-if="isShow">
  </p>
 </transition>
</template>
<script type="text/babel">
 export default {
  data() {
   return {
    isShow: true, // 是否显示进度条
    val: 0, // 进度
   }
  },
  props: {
   /**
    * 每10毫秒自增幅度
    */
   step: {
    type: Number,
    default: 5,
   },
   /**
    * 初始值
    */
   initVal: {
    type: Number,
    default: 0,
   },
   /**
    * 到一定进度停止
    */
   stopVal: {
    type: Number,
    default: 80,
   },
   /**
    * 进度条继续到成功
    */
   isOk: {
    type: Boolean,
    default: false,
   },
  },
  mounted() {
   // 初始化后加载进度，加载到百分之多少由stopVal决定
   this.val = this.initVal
   let step = this.step
   let timer = setInterval(() => {
    this.val = this.val + step
    this.$el.style.width = this.val + &#39;%&#39;
    // 父组件数据加载完前进度条最多到stopVal的这个百分值
    if (this.val >= this.stopVal) {
     clearInterval(timer)
     return
    }
   }, 10)
  },
  watch: {
   /**
    * 监听组件props变化决定是否继续加载，一般在父组件数据加载完后改变此标志位
    */
   isOk() {
    let val = this.val
    let step = this.step
    let timer = setInterval(() => {
     val = val + step
     this.$el.style.width = val + &#39;%&#39;
     // 加载到百分百完成
     if (val >= 100) {
      // 关闭定时器
      clearInterval(timer)
      // 加载完成关闭进度条
      this.isShow = false
      // 加载完成的回调
      this.$emit(&#39;callback&#39;, &#39;load success&#39;)
      return
     }
    }, 10)
   },
  },
 }
</script>
<style lang="stylus" rel="stylesheet/stylus">
 .progress-bar {
  position fixed
  top 0
  height 6px
  width 0
  background-color #999
 }
 .fade {
  &-enter-active, &-leave-active {
   transition: all .3s
  }
  &-enter, &-leave-active {
   opacity: 0
  }
 }
</style>

The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.

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