原创是https://blog.csdn.net/liujava621/article/details/30495103，我这里做了修改，侵权删。
上干货：这里首先要注意操作四个角的时候，框的长宽会变化，同时绝对定位的top，left可能随之变化，我之前就犯了错误，导致移动过程框的大小变了，位置也变化了
<!DOCTYPE html> <html> <head> <meta charset="utf-8" /> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <title>Page Title</title> <meta name="viewport" content="width=device-width, initial-scale=1"> <style> body{ display: flex; justify-content: center; flex-direction: column; align-items: center; } /* .main{ position: relative; width: 400px; height: 200px; border: 1px solid red; } .main span:nth-child(1){ position: absolute; left: -5px; top: -5px; padding: 15px; border-style: solid; border-color: rebeccapurple; border-width: 5px 0 0 5px; } .main span:nth-child(2){ position: absolute; right: -5px; top: -5px; padding: 15px; border-style: solid; border-color: rebeccapurple; border-width: 5px 5px 0 0; } .main span:nth-child(3){ position: absolute; right: -5px; bottom: -5px; padding: 15px; border-style: solid; border-color: rebeccapurple; border-width: 0 5px 5px 0; } .main span:nth-child(4){ position: absolute; left: -5px; bottom: -5px; padding: 15px; border-style: solid; border-color: rebeccapurple; border-width: 0 0 5px 5px; } */ .box{ width:200px; height:200px; border:1px solid gray; position:absolute; left:200px; top:100px; } .upleftbtn,.uprightbtn,.downleftbtn,.downrightbtn{ width:10px; height:10px; border:1px solid steelblue; position: absolute; z-index:5; background: whitesmoke; } .upleftbtn{ top:-5px; left:-5px; cursor:nw-resize; } .uprightbtn{ top:-5px; right:-5px; cursor:ne-resize; } .downleftbtn{ left:-5px; bottom:-5px; cursor:sw-resize; } .downrightbtn{ right:-5px; bottom:-5px; cursor:se-resize; } </style> <script> var obj = null;//当前操作对象 var box = null;//要处理的对象; //保留上次的x,y位置 var clickX = 0; var clickY = 0; //鼠标点击 var onDragDown = function(e,type){ e = e ||window.event; var location = { x:e.x || e.clientX, y:e.y || e.clientY } clickX = e.x || e.clientX; clickY = e.y || e.clientY; obj = this; obj.operateType = type; box = document.getElementById("box"); return false; } var onBoxDragDown = function(e,type){ e = e ||window.event; var location = { x:e.x || e.clientX, y:e.y || e.clientY } clickX = e.x || e.clientX; clickY = e.y || e.clientY; obj = this; obj.operateType = type; box = document.getElementById("box"); return false; } var onUpleftbtn = function(e){ e.stopPropagation(); onDragDown(e, "nw"); } var onUpRightbtn = function(e){ e.stopPropagation(); onDragDown(e, "ne"); } var onDownleftbtn = function(e){ e.stopPropagation(); onDragDown(e, "sw"); } var onDownRightbtn = function(e){ e.stopPropagation(); onDragDown(e, "se"); } var onBoxDown = function(e){ onBoxDragDown(e, "move"); } var move = function(type,location,tarobj){ switch(type) { case 'n': var add_length = clickY - location.y; clickY = location.y; var length = parseInt(tarobj.style.height) + add_length; tarobj.style.height = length + "px"; tarobj.style.top = clickY + "px"; break; case 's': var add_length = clickY - location.y; clickY = location.y; var length = parseInt(tarobj.style.height) - add_length; tarobj.style.height = length + "px"; break; case 'w': var add_length = clickX - location.x; clickX = location.x; var length = parseInt(tarobj.style.width) + add_length; tarobj.style.width = length + "px"; tarobj.style.left = clickX + "px"; break; case 'e': var add_length = clickX - location.x; clickX = location.x; var length = parseInt(tarobj.style.width) - add_length; tarobj.style.width = length + "px"; break; case 'move': var add_ylength = clickY - location.y; clickY = location.y; var length = parseInt(tarobj.style.top) - add_ylength; // tarobj.style.height = length + "px"; tarobj.style.top = length + "px"; var add_xlength = clickX - location.x; clickX = location.x; var xlength = parseInt(tarobj.style.left) - add_xlength; // tarobj.style.width = length + "px"; tarobj.style.left = xlength + "px"; break; } } window.onload = function(e){ document.getElementById("upleftbtn").onmousedown = onUpleftbtn; document.getElementById("uprightbtn").onmousedown = onUpRightbtn; document.getElementById("downleftbtn").onmousedown = onDownleftbtn; document.getElementById("downrightbtn").onmousedown = onDownRightbtn; document.getElementById("box").onmousedown = onBoxDown; document.onmousemove = function(e){ if(obj) { e = e || window.event; var location = { x:e.x || e.clientX, y:e.y || e.clientY } switch(obj.operateType) { case "nw": move('n',location,box); move('w',location,box); break; case "ne": move('n',location,box); move('e',location,box); break; case "sw": move('s',location,box); move('w',location,box); break; case "se": move('s',location,box); move('e',location,box); break; case "move": move('move',location,box); break; } } } document.onmouseup = function(){ document.body.style.cursor = "auto"; obj = null; } } </script> </head> <body> <div class="box" id="box" style="width:200px; height:200px;left:200px; top:100px;"> <div class="upleftbtn" id="upleftbtn"></div> <div class="uprightbtn" id="uprightbtn"></div> <div class="downleftbtn" id="downleftbtn"></div> <div class="downrightbtn" id="downrightbtn"></div> </div> </body> </html>转载于:https://www.cnblogs.com/zimingche/p/9270761.html
相关资源：一个简单的JS画矩形代码