Element InputNumber 计数器的实现示例

<el-input-number v-model="num" @change="handleChange" :min="1" :max="10" label="描述文字">
</el-input-number>

<template>
 <div
 :class="[
  'el-input-number',
 ]"
 >
 <span 
  class="el-input-number__decrease"
  role="button"
  :class="{'is-disabled': minDisabled}"
  @click="decrease"
 >
  <i class="el-icon-minus"></i>
 </span>
 <span
  class="el-input-number__increase"
  role="button"
  :class="{'is-disabled': maxDisabled}"
  @click="increase"
 >
  <i class="el-icon-plus"></i>
 </span>
 <el-input
  ref="input"
  :value="value"
  @input="value => $emit('input', value)"
 >
 </el-input>
 </div>
</template>

<script>
import ElInput from '../Input/index'

export default {
 name: 'ElInputNumber',
 props: {
 value: {},
 max: {
  type: Number,
  default: Infinity
 },
 min: {
  type: Number,
  default: -Infinity
 },
 },
 computed: {
 minDisabled() {
  return this.value - 1 < this.min;
 },
 maxDisabled() {
  return this.value + 1 > this.max;
 },
 },
 methods: {
 decrease() {
  if(this.minDisabled) return

  this.$emit('input', this.value - 1)
 },
 increase() {
  if(this.maxDisabled) return

  this.$emit('input', this.value + 1)
 }
 },
 components: {
 ElInput
 }
}
</script>

import { once, on } from '../utils/dom';

export default {
 bind(el, binding, vnode) {
 let interval = null;
 let startTime;
 // binding.expression 就是decrease/increase 事件名称
 // handler就是对应的相应函数
 const handler = () => vnode.context[binding.expression].apply();
 const clear = () => {
  if (Date.now() - startTime < 100) {
  handler();
  }
  clearInterval(interval);
  interval = null;
 };

 on(el, 'mousedown', (e) => {
  if (e.button !== 0) return;
  startTime = Date.now();
  once(document, 'mouseup', clear);
  clearInterval(interval);
  // 实现节流
  interval = setInterval(handler, 100);
 });
 }
};

import RepeatClick from '../../directives/repeat-click';

directives: {
 repeatClick: RepeatClick
},

<span 
 class="el-input-number__decrease"
 role="button"
 :class="{'is-disabled': minDisabled}"
 v-repeat-click="decrease"
>
 <i class="el-icon-minus"></i>
</span>
<span
 class="el-input-number__increase"
 role="button"
 :class="{'is-disabled': maxDisabled}"
 v-repeat-click="increase"
>
 <i class="el-icon-plus"></i>
</span>

<el-input-number v-model="num" :step="2"></el-input-number>

 <el-input-number v-model="num" :step="2" step-strictly></el-input-number>

data() {
 return {
 currentValue: 0, // 缓存上次输入的值
 userInput: null, // 缓存当前输入的值
 };
},

<el-input
 ref="input"
 :disabled="disabled"
 :value="currentValue" // 变为绑定currentValue
 @input="handleInput"
 @change="handleInputChange"
>
</el-input>

// 先在el-input的input事件记录输入的值
handleInput(value) {
 this.userInput = value;
},
// 在change事件中将值赋予给value
handleInputChange(value) {
 let newVal = value === '' "color: #ff0000">精度

上测试代码：


<el-input-number v-model="numPrecision" :precision="2" :step="0.1" :max="10"></el-input-number>


这里step变成小数了，那在累加得过程中，就会有0.1+0.2这样得精度问题出现了。element的解决思路是将值扩大精度倍进行计算，得到结果后再除以精度倍数。


increase() {
 if(this.maxDisabled || this.disabled) return
 const value = this.value || 0;
 const newVal = this._increase(value, this.step);

 this.setCurrentValue(newVal);
},
_increase(val, step) {
 if (typeof val !== 'number' && val !== undefined) return this.currentValue;
 // step是0.1，precisionFactor是10。
 const precisionFactor = Math.pow(10, this.numPrecision);

 return this.toPrecision((precisionFactor * val + precisionFactor * step) / precisionFactor);
},

// 确保计算得结果0.10000000001这种误差情况会被消除
 toPrecision(num, precision) {
 if (precision === undefined) precision = this.numPrecision;
 return parseFloat(Math.round(num * Math.pow(10, precision)) / Math.pow(10, precision));
},


在展示的时候，利用toFixed函数展示精度即可。
效果如下：

尺寸
添加size属性，在根元素得样式添加size "text-align: center">
按钮位置
设置 controls-position 属性可以控制按钮位置。
上测试代码：


<el-input-number v-model="num" controls-position="right" @change="handleChange" :min="1" :max="10">
</el-input-number>


通过controls-position='right'，在组件内控制样式即可。
效果如下：

总结
严格步数和精度这两个特性得逻辑稍有些复杂，需要多研究一会。
源码在码云： https://gitee.com/DaBuChen/my-element-ui/tree/input-number