本文展示了將香草JavaScript倒數(shù)計(jì)時(shí)器重構(gòu)為可重複使用的VUE組件。原始計(jì)時(shí)器在上一篇文章中詳細(xì)介紹，缺乏可重複性和有效的UI同步。這種轉(zhuǎn)換解決了這些缺點(diǎn)。

為什麼要使用vue？主要是有兩個(gè)原因：

• 同步UI和計(jì)時(shí)器狀態(tài)：原始javaScript代碼在timerInterval函數(shù)中託管狀態(tài)，直接操縱DOM元素。 Vue的模板語法聲明將DOM綁定到組件的數(shù)據(jù)，簡化了UI更新。
• 可重用性：原始計(jì)時(shí)器依賴於元素ID，從而限制了其可重複使用性。 VUE組件封裝了其邏輯，從而在單個(gè)頁面上啟用了多個(gè)獨(dú)立的計(jì)時(shí)器實(shí)例。

這是VUE實(shí)施：

模板和樣式

VUE使用基於HTML的模板系統(tǒng)。我們將創(chuàng)建一個(gè)帶有以下結(jié)構(gòu)的BaseTimer.vue文件：

<code><template>
  
</template>

<script>
  // ...
</script>

<style scoped>
  /* ... */
</style></code>

這<template></template>部分包含計(jì)時(shí)器的標(biāo)記（主要是上一篇文章中的SVG），

<template>
  <div class="base-timer">
    <svg viewbox="0 0 100 100" xmlns="http://www.w3.org/2000/svg">
      <g>
        <circle cx="50" cy="50" r="45"></circle>
        <path :class="remainingPathColor" :stroke-dasharray="circleDasharray" d="
            M 50, 50
            m -45, 0
            a 45,45 0 1,0 90,0
            a 45,45 0 1,0 -90,0
          "></path>
      </g>
    </svg>
    {{ formattedTimeLeft }}
  </div>
</template>

<style scoped>
.base-timer {
  position: relative;
  width: 100px;
  height: 100px;
}
</style>計(jì)時(shí)器的關(guān)鍵方面是通過數(shù)據(jù)綁定來控制的： <code>stroke-dasharray</code> ， <code>remainingPathColor</code>和<code>formatTime(timeLeft)</code> 。<h3>常數(shù)和變量</h3><p>這<script> section defines constants and variables.  Constants, such as <code>FULL_DASH_ARRAY, <code>WARNING_THRESHOLD, <code>ALERT_THRESHOLD, and <code>COLOR_CODES, are defined directly.</script></p>
<p>Variables are categorized: those directly re-assigned in methods (<code>timerInterval</code>, <code>timePassed</code>) and those dependent on other variables (<code>timeLeft</code>, <code>remainingPathColor</code>).</p>
<h4>Reactive Variables</h4>
<p>Variables directly modified in methods are declared within the <code>data()</code> method to leverage Vue's reactivity system:</p>
<pre class="brush:php;toolbar:false">data() {
  return {
    timePassed: 0,
    timerInterval: null
  };
},

Computed Properties

Variables dependent on other variables are implemented as computed properties:

computed: {
  timeLeft() {
    return TIME_LIMIT - this.timePassed;
  },
  circleDasharray() {
    return `${(this.timeFraction * FULL_DASH_ARRAY).toFixed(0)} 283`;
  },
  formattedTimeLeft() {
    // ... (time formatting logic) ...
  },
  timeFraction() {
    // ... (time fraction calculation) ...
  },
  remainingPathColor() {
    // ... (color calculation based on timeLeft) ...
  }
},

Computed properties are pure functions, cached for efficiency.

Using Data and Computed Properties in the Template

The template utilizes text interpolation ({{ ... }}) and v-bind (or its shorthand :) directives to dynamically bind data and computed properties to the DOM.

Methods and Lifecycle Hooks

The startTimer method, simplified due to the use of computed properties, is called within the mounted() lifecycle hook:

methods: {
  startTimer() {
    this.timerInterval = setInterval(() => (this.timePassed  = 1), 1000);
  }
},
mounted() {
  this.startTimer();
},

Component Usage

To use the BaseTimer component in another component (e.g., App.vue):

1. Import: import BaseTimer from "./components/BaseTimer";
2. Register: components: { BaseTimer }
3. Instantiate: <basetimer></basetimer> in the template.

This refactoring demonstrates the benefits of using Vue components for improved code organization, reusability, and efficient state management. The resulting component is self-contained and easily integrated into larger applications.

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