4 custom instructions worth knowing about in vue (practical sharing)

In addition to the default core directives (v-model and v-show), Vue also allows the registration of custom directives. This article will share with you four practical vue custom instructions. I hope it will be helpful to you.

Four practical vue custom instructions

1, v-drag

Requirement: mouse drag element

Idea:

• Element offset = mouse sliding The coordinates after - the coordinates when the mouse initially clicks on the element. The distance between the element and the top and left of the visible area when the initial click is made.
• Use the visible area as the boundary and limit dragging within the visible area. [Related recommendations: "vue.js Tutorial"]

Code:

Vue.directive('drag', {
  inserted(el) {
    let header = el.querySelector('.dialog_header')
    header.style.cssText += ';cursor:move;'
    header.onmousedown = function (e) {
      //获取当前可视区域宽、高
      let clientWidth = document.documentElement.clientWidth
      let clientHeight = document.documentElement.clientHeight

      //获取自身宽高
      let elWidth = el.getBoundingClientRect().width
      let elHeight = el.getBoundingClientRect().height

      //获取当前距离可视区域的top、left
      let elTop = el.getBoundingClientRect().top
      let elLeft = el.getBoundingClientRect().left

      //获取点击时候的坐标
      let startX = e.pageX
      let startY = e.pageY

      document.onmousemove = function (e) {
        //元素偏移量 = 鼠标滑动后的坐标 - 鼠标初始点击元素时的坐标 + 初始点击时元素距离可视区域的top、left
        let moveX = e.pageX - startX + elLeft
        let moveY = e.pageY - startY + elTop

        //将可视区域作为边界，限制在可视区域里面拖拽
        if ((moveX + elWidth) > clientWidth || moveX < 0 || (moveY + elHeight) > clientHeight || moveY < 0) {
          return
        }

        el.style.cssText += &#39;top:&#39; + moveY + &#39;px;left:&#39; + moveX + &#39;px;&#39;
      }
      document.onmouseup = function () {
        document.onmousemove = null
        document.onmouseup = null
      }
    }
  }
})

##2, v-wordlimit

Requirements: The background field limits the length and distinguishes between Chinese and English, two bytes for Chinese and one byte for English; Therefore, the input box needs to limit the number of words entered and distinguish the number of bytes, and it needs to echo the number of words entered.

Idea:

One byte regular/[\x00-\xff]/g
Create an element that wraps the word limit, and position the layout in textarea and On the input box,
respectively calculates the input characters for one byte, enLen, and two bytes, cnLen; used for subsequent string truncation processing
When the number of input characters exceeds the limit The number of words, truncation processing; substr(0,enLen cnLen)
The interface updates the value of the input box, or initializes the value of the input box, and needs to echo the correct number of bytes

Code:

Vue.directive('wordlimit',{
  bind(el,binding){
    console.log('bind');
    let { value } = binding
    Vue.nextTick(() =>{
      //找到输入框是textarea框还是input框
      let current = 0
      let arr = Array.prototype.slice.call(el.children)
      for (let i = 0; i < arr.length; i++) {
        if(arr[i].tagName==&#39;TEXTAREA&#39; || arr[i].tagName==&#39;INPUT&#39;){
          current = i
        }
      }
  
      //更新当前输入框的字节数
      el.children[el.children.length-1].innerHTML = el.children[current].value.replace(/[^\x00-\xff]/g,&#39;**&#39;).length +&#39;/&#39;+value//eslint-disable-line
    })
  },
  update(el,binding){
    console.log(&#39;update&#39;);
    let { value } = binding
    Vue.nextTick(() =>{
      //找到输入框是textarea框还是input框
      let current = 0
      let arr = Array.prototype.slice.call(el.children)
      for (let i = 0; i < arr.length; i++) {
        if(arr[i].tagName==&#39;TEXTAREA&#39; || arr[i].tagName==&#39;INPUT&#39;){
          current = i
        }
      }
  
      //更新当前输入框的字节数
      el.children[el.children.length-1].innerHTML = el.children[current].value.replace(/[^\x00-\xff]/g,&#39;**&#39;).length +&#39;/&#39;+value//eslint-disable-line
    })
  },
  inserted(el,binding){
    console.log(&#39;inserted&#39;);
    let { value } = binding

    //找到输入框是textarea框还是input框
    let current = 0
    let arr = Array.prototype.slice.call(el.children)
    for (let i = 0; i < arr.length; i++) {
      if(arr[i].tagName==&#39;TEXTAREA&#39; || arr[i].tagName==&#39;INPUT&#39;){
        current = i
      }
    }

    //创建包裹字数限制的元素，并定位布局在textarea和input框上
    let div = document.createElement(&#39;div&#39;)
    if(el.children[current].tagName==&#39;TEXTAREA&#39;){//是textarea，定位在右下角
      div.style = &#39;color:#909399;position:absolute;font-size:12px;bottom:5px;right:10px;&#39;
    }else{
      let styStr = &#39;&#39;
      if(!el.classList.contains(&#39;is-disabled&#39;)){//input框不是置灰的状态则添加背景颜色
        styStr = &#39;background:#fff;&#39;
      }
      div.style = &#39;color:#909399;position:absolute;font-size:12px;bottom:2px;right:10px;line-height:28px;height:28px;&#39;+styStr
    }

    div.innerHTML = &#39;0/&#39;+ value
    el.appendChild(div)
    el.children[current].style.paddingRight = &#39;60px&#39;

    el.oninput = () =>{
      let val = el.children[current].value
      val = val.replace(/[^\x00-\xff]/g,&#39;**&#39;) //eslint-disable-line
      // 字数限制的盒子插入到el后是最后一个元素
      el.children[el.children.length-1].innerHTML = val.length + &#39;/&#39; + value
      if(val.length>value){
        let cnLen = 0 //一个字节的字数
        let enLen = 0 //两个字节的字数

        if(val.match(/[^**]/g) && val.match(/[^**]/g).length){
          enLen = val.match(/[^**]/g).length // 计算一个字节的字数

          //一个字节两个字节都有的情况
          if((value - val.match(/[^**]/g).length)>0){
            cnLen = Math.floor((value - val.match(/[^**]/g).length)/2)
          }else{
            cnLen = 0
          }
        }else{ //全部两个字节的情况
          enLen = 0
          cnLen = Math.floor(value/2)
        }

        if(enLen>value){
          enLen = value
        }

        //超过限定字节数则截取
        el.children[current].value = el.children[current].value.substr(0,enLen+cnLen)

        //更新当前输入框的字节数
        el.children[el.children.length-1].innerHTML = el.children[current].value.replace(/[^\x00-\xff]/g,&#39;**&#39;).length +&#39;/&#39;+value//eslint-disable-line

      }
    }

  },
})

Use:

<el-input type="textarea" rows="3" v-wordlimit="20" v-model="value"></el-input>

3、v-anthor

Requirements: Click on an element (usually a title, subtitle, etc.), and the animation will scroll to the corresponding content block

Idea:

The timer uses window. scrollBy
If you do not consider ie, you can directly use window.scrollBy({ top: ,left:0,behavior:'smooth' })

Code:

Vue.directive('anchor',{
  inserted(el,binding){
    let { value } = binding
    let timer = null
    el.addEventListener('click',function(){
      // 当前元素距离可视区域顶部的距离
      let currentTop = el.getBoundingClientRect().top
      animateScroll(currentTop)
    },false)
    
    function animateScroll(currentTop){
      if(timer){
        clearInterval(timer)
      }
      let c = 9
      timer = setInterval(() =>{
        if(c==0){
          clearInterval(timer)
        }
        c--
        window.scrollBy(0,(currentTop-value)/10)
      },16.7)
    }

  }
})

Use:

<div class="box" v-anchor="20" style="color:red;">是的</div>

4, v-hasRole##Requirements: According to the system Add or delete corresponding elements to the role

Code:

Vue.directive('hasRole',{
  inserted(el,binding){
    let { value } = binding
    let roles = JSON.parse(sessionStorage.getItem('userInfo')).roleIds

    if(value && value instanceof Array && value.length>0){

      let hasPermission = value.includes(roles)

      if(!hasPermission){
        el.parentNode && el.parentNode.removeChild(el)
      }
    }else{
      throw new Error(`请检查指令绑定的表达式，正确格式例如 v-hasRole="['admin','reviewer']"`)
    }
  }
})

For more programming-related knowledge, please visit:

Introduction to Programming

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