input 字符串长度限制，中文字符算两个

Vue封装常用指令Directive

<a-input  v-model="inputValue"  @change="onChange" style="width:300px"/>

onChange(e) {
        let str = e.target.value

        // 字符串长度限制，中文字符算两个
          str = str.slice(0,this.maxLength)
          let endIndex = 0
          if(getBLen(str) > this.maxLength){
            let dist = getBLen(str) - str.length
            endIndex = this.maxLength - (~~(dist/2)) - (dist%2)
            str = str.slice(0,endIndex)
          }

          // 还是大于最大值，存在临界状态
          if(getBLen(str) > this.maxLength){
            str = str.slice(0,(endIndex - 1))
          }

        this.inputValue = str
      },

// 判断字符串长度（英文占1个字符，中文汉字占2个字符）
export function getBLen(str) {
  let len = 0;
  for (let i=0; i<str.length; i++) {
    if (str.charCodeAt(i)>127 || str.charCodeAt(i)==94) {
      len += 2;
    } else {
      len ++;
    }
  }
  return len;
}

// 防抖
export function _debounce(fn, delay) {
  var delay = delay || 200
  var timer
  return function() {
    var _this = this
    var args = arguments
    if (timer) {
      clearTimeout(timer)
    }
    timer = setTimeout(function() {
      timer = null
      fn.apply(_this, args)
    }, delay)
  }
}

封装指令

import { getBLen } from '@/utils/util'
import { _debounce } from '@/utils/util.js'

// input 字符串长度限制，中文字符算两个
const maxLength = {
  bind:function (el, binding) {
    let flag = false
    let oldStr = ''
    el.addEventListener('compositionstart',function () {
      flag = true
    })
    el.addEventListener('compositionend',function () {
      flag = false
    })
    el.addEventListener('input', _debounce(() => {
      if(flag) return

      let str = el.value
      const maxLength = binding.value
      str = str.slice(0, maxLength)
      let endIndex = 0
      if(getBLen(str) > maxLength){
        let dist = getBLen(str) - str.length
        endIndex = maxLength - (~~(dist/2)) - (dist%2)
        str = str.slice(0,endIndex)
      }

      // 还是大于最大值，存在临界状态
      if(getBLen(str) > maxLength){
        str = str.slice(0,(endIndex - 1))
      }

      el.value = str
      // 避免反复触发
      if(oldStr != el.value){
        el.dispatchEvent(new Event('input'))
        oldStr = el.value
      }
    }, 50))
  }
}

Vue.directive('maxLength', maxLength)