元素可拖拽（移动端与pc端）

　　项目中经常遇到这种需求，特此记录下：

　　css部分：

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<style>     #target {         width: 200px;     height: 200px;     border-radius: 6px;     background: #eee;     position: absolute;     } </style>

　　

　　html部分：

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1	<div id="target"></div>

　　

　　js部分（这里分了两种情况，因为pc端与移动端的处理情况有点不太一样）：

　　（1）、pc端

const winW = window.innerWidth
const winH = window.innerHeight 
const target = document.getElementById('target')
const targetW = target.offsetWidth
const targetH = target.offsetHeight
const maxL = winW - targetW           // 距离左侧的最大距离
const maxT = winH - targetH           // 距离顶部的最大距离
let posArr = []
        
target.addEventListener('mousedown', function (e) {
    posArr = [e.clientX, e.clientY]   
})

document.addEventListener('mousemove', function (e) {
    let [x, y] = [e.clientX, e.clientY]  
    const deltaX = x - posArr[0]        // 移动的水平距离
    const deltaY = y - posArr[1]        // 移动的垂直距离
    const left = parseInt(target.style.left || 0)   // 如果值不存在时，赋默认值很关键，不然值为NaN
    const top = parseInt(target.style.top || 0)
    let [moveX, moveY] = ['', '']
    if (left + deltaX > maxL) {
    moveX = maxL
    } else if (left + deltaX >= 0 && left + deltaX <= maxL) {
    moveX = left + deltaX
    } else {
    moveX = 0
    }

    if (top + deltaY > maxT) {
    moveY = maxT
    } else if (top + deltaY >= 0 && top + deltaY <= maxT) {
    moveY = top + deltaY
    } else {
    moveY = 0
    }
    target.style.left = moveX + 'px'
    target.style.top = moveY + 'px'
    posArr = [x, y]
})

 

　　(2)、移动端，情况稍微有点不一样，监听的事件为touch事件，其次获取元素当前位置也有点不一样，具体代码：

const winW = window.innerWidth
const winH = window.innerHeight 
const target = document.getElementById('target')
const targetW = target.offsetWidth
const targetH = target.offsetHeight
const maxL = winW - targetW           // 距离左侧的最大距离
const maxT = winH - targetH           // 距离顶部的最大距离
let posArr = []
        
target.addEventListener('touchstart', function (e) {
    posArr = [e.changedTouches[0].clientX, e.changedTouches[0].clientY]
})

document.addEventListener('touchmove', function (e) {
    let [x, y] = [e.changedTouches[0].clientX, e.changedTouches[0].clientY]
    const deltaX = x - posArr[0]        // 移动的水平距离
    const deltaY = y - posArr[1]        // 移动的垂直距离
    const left = parseInt(target.style.left || 0)   // 如果值不存在时，赋默认值很关键，不然值为NaN
    const top = parseInt(target.style.top || 0)
    let [moveX, moveY] = ['', '']
    if (left + deltaX > maxL) {
    moveX = maxL
    } else if (left + deltaX >= 0 && left + deltaX <= maxL) {
    moveX = left + deltaX
    } else {
    moveX = 0
    }
    if (top + deltaY > maxT) {
    moveY = maxT
    } else if (top + deltaY >= 0 && top + deltaY <= maxT) {
    moveY = top + deltaY
    } else {
    moveY = 0
    }
    target.style.left = moveX + 'px'
    target.style.top = moveY + 'px'
    posArr = [x, y]
})