[Input-number]數字輸入框組件

需求

• 加、減按鈕
• 初始值
• 最大、最小值
• 數值改變時，觸發一個自定義事件來通知父組件

目錄文件

• index.html 入口頁
• input-number.js 數字輸入框組件
• index.js 根實例

實現關鍵

• Vue組件是單向數據流，無法從組件內部直接修改prop的值，解決辦法就是給組件生命一個data，默認引用prop值，然后在組件內部維護這個data

  Vue.component('input-number', {
    data: function () {
        return {
            currentValue: this.value // value來自props里的屬性
        }
    }
  });
  

• 上述解決了初始化引用父組件value的問題，但如果父組件更新了value，input-number組件中的currentValue也需要一起更新

  1. 為了實現同步更新的功能，我們需要使用 watch 監聽功能(watch選項可以用來監聽某個prop或data的改變，並在它們發送改變時，觸發watch配置的函數)

  2. 在這里我們要監聽兩個數據，value和currentView；監聽value是為了得知父組件修改了value，監聽currentValue是為了當currentValue改變時，更新value

• input中綁定currentValue值，當用戶輸入結束時使用change事件來更新currentValue，這里不是用input事件(input事件是實時的，change事件是失焦時，從性能上來說change好很多)

• 使用watch選項來監聽value與currentValue的改變

  watch: {
        value: function (val) {
            this.updateValue(val);
        },
        currentValue: function (val) {
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word-break: inherit !important;">t<span class="mord mathit" style="font-size: inherit; color: inherit; line-height: inherit; margin: 0px; padding: 0px; word-wrap: inherit !important; word-break: inherit !important;">h<span class="mord mathit" style="font-size: inherit; color: inherit; line-height: inherit; margin: 0px; padding: 0px; word-wrap: inherit !important; word-break: inherit !important;">i<span class="mord mathit" style="font-size: inherit; color: inherit; line-height: inherit; margin: 0px; padding: 0px; word-wrap: inherit !important; word-break: inherit !important;">s<span class="mord" style="font-size: inherit; color: inherit; line-height: inherit; margin: 0px; padding: 0px; word-wrap: inherit !important; word-break: inherit !important;">.emit('on-change', val);
        }
  }
  

  雖然也可以在每個會引起currentValue改變的函數中(加、減、輸入等方法)向父組件拋出值，但是使用watch可以減少代碼的冗余

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