JS拖拽组件开发 · 致力于web前端技术撰写

JS代码需要常写，不然容易生疏，最近虽然一直在看JS的原型，行为委托等知识点，但是动手写代码的量略有减少。周末在家，写了一个拖拽组件，与大家分享。首先，看一下拖拽的原理。 ![这里写图片描述](https://box.kancloud.cn/2016-04-07_570603f195dd1.jpg "") 被拖拽元素位置的变化，left值的变化其实就是鼠标位置水平方向的变化值，e.clientX - 鼠标左键按下时e.clientX。 top值的变化其实就是鼠标位置竖直方向的变化值，e.clientY - 鼠标左键按下时e.clientY。另外就是设置拖拽的范围，上下左右不得超过父元素所在的区域。 ~~~ function Drag (config){ this.moveTarget = document.getElementById(config.id); if(config.parentId){ this.targetParent = document.getElementById(config.parentId); this.max_left = this.targetParent.clientWidth - this.moveTarget.offsetWidth; this.max_top = this.targetParent.clientHeight - this.moveTarget.offsetHeight; }else{ console.log(document.documentElement.clientHeight + "||" + this.moveTarget.offsetHeight) this.max_left = document.documentElement.clientWidth - this.moveTarget.offsetWidth - parseInt(this.getStyle(document.body, "border-width")); this.max_top = document.documentElement.clientHeight - this.moveTarget.offsetHeight- parseInt(this.getStyle(document.body, "border-width")); } this.lock = true; } Drag.prototype.getStyle = function(element, attr){ if(element.currentStyle){ return element.currentStyle[attr]; }else{ return window.getComputedStyle(element,null).getPropertyValue(attr) } } Drag.prototype.moDown = function(e){ e = e || window.event; this.clientX = e.clientX; this.clientY = e.clientY; //鼠标按下时，drag的left值，top值(写在style中或者是css中) this.startLeft = parseInt(this.moveTarget.style.left || this.getStyle(this.moveTarget, "left")); this.startTop = parseInt(this.moveTarget.style.top || this.getStyle(this.moveTarget, "top")); //鼠标按下时，鼠标的clientX值，clientY值 this.startClientX = e.clientX; this.startClientY = e.clientY; this.lock = false; }; Drag.prototype.moMove = function(e){ e = e || window.event; if(e.which != 1){ this.lock = true; } if(!this.lock){ var realLeft = this.startLeft + e.clientX - this.startClientX;//实际的移动范围 var realTop = this.startTop + e.clientY - this.startClientY; //rightLeft , rightTop; //left, top 取值(在可移动范围内) var rightLeft = realLeft > this.max_left ? this.max_left : ( realLeft > 0 ? realLeft : 0 ); var rightTop = realTop > this.max_top ? this.max_top : ( realTop > 0 ? realTop : 0 ); this.moveTarget.style.left = rightLeft + "px"; this.moveTarget.style.top = rightTop + "px"; } }; Drag.prototype.moUp = function(e){ e = e || window.event; this.lock = true; }; Drag.prototype.startDrag = function(){ console.log(this) this.moveTarget.onmousedown = function(e){this.moDown(e)}.bind(this); this.moveTarget.onmousemove = function(e){this.moMove(e)}.bind(this); this.moveTarget.onmouseup = function(e){this.moUp(e)}.bind(this); } ~~~ 说明：moDown响应鼠标左键按下操作，moMove响应鼠标移动操作，MoUp响应鼠标抬起操作。在moMove中增加了e.which判断，e.which ==1 表示鼠标左键按下，这是为了解决，鼠标移除可拖拽范围外，再移回时，无需按下左键，被拖拽元素就会跟着动的Bug。使用说明：在使用时，被拖拽元素的id是必须参数，父元素的id(即可以拖拽移动的范围)为可选参数，如果不传递父元素的id，则默认使用documentElement为可拖拽的范围。如果传递父元素，请别忘了将父元素的定位设为position:relative或position:absolute。在使用时，先引入拖拽插件的js文件。 ~~~ <!doctype html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="Generator" content="EditPlus®"> <meta name="Author" content="刘艳"> <meta name="Keywords" content="关键字"> <meta name="Description" content="描述"> <title>Document</title> <style> *{ margin:0px; padding:0px; } #content{ width:600px; height:500px; position:relative; border:5px solid green; } #drag{ position:absolute; height:100px; width:100px; top:50px;left:0px; background:pink; cursor:pointer; } </style> </head> <body> <div id = "content"> <div id = "drag" > </div> </div> </body> </html> <script src = "url/drag.js"></script> <script> window.onload = function(){ var drag = new Drag({id: "drag", parentId: "content"}); drag.startDrag(); } </script> ~~~ 如果您想在整个窗口中拖拽，请不要设置被拖拽元素的父元素的定位，即，使其相对body定位。如果您需要对body定位，但是又需要设置其父元素的position为非static，那么您可以对本插件进行扩展。希望本文对您JS的学习能有所帮助。