js拖拽的常见思路

1.通过onmousedown,onmousemove,onmouseup分别模拟开始拖拽，拖拽中和拖拽结束时的事件（）。

如果手机的触摸事件的话则分别是ontouchstart,ontouchmove和ontouchend。

2.鼠标按下即发生onmousedown事件时：获取鼠标位置，获取被拖动元素的位置，记录两者之间的纵横坐标的差值（）。对document元素绑定onmousemove,onmouseup事件。

刚开始接触js拖拽时，我当时疑惑的是为什么是对document绑定而不是对被拖动的元素绑定呢？原来是如果对被拖动元素绑定的话当鼠标拖动过快时，会导致鼠标与被拖动元素的脱离。

3.鼠标拖动即发生onmousemove事件时：将被拖拽元素的position改成绝对位置，这个可以通过left和top改变该元素的位置，从而使得该元素随着鼠标的拖拽而移动。获取鼠标位置，将鼠标x坐标（e.clientX）减去第2步储存的横坐标差作为被拖动元素的left值，将鼠标x坐标（e.clientY）减去第2步储存的纵坐标差作为被拖动元素的top值。实现元素跟随鼠标拖动的效果。

4.鼠标按键弹起即发生onmouseup事件时：清空onmousemove和onmouseup事件

比较流行的拖拽插件dom-drag类库（作者： Aaron Boodman）

其源代码如下
复制代码 代码如下:
/*其中( dom-drag.js )文件**************************************************
* dom-drag.js
* 09.25.2001
* www.youngpup.net
**************************************************
* 10.28.2001 - fixed minor bug where events
* sometimes fired off the handle, not the root.
**************************************************/

var Drag = {

obj : null,

init : function(o, oRoot, minX, maxX, minY, maxY, bSwapHorzRef, bSwapVertRef, fXMapper, fYMapper)
{
o.onmousedown = Drag.start;

o.hmode = bSwapHorzRef ? false : true ;
o.vmode = bSwapVertRef ? false : true ;

o.root = oRoot && oRoot != null ? oRoot : o ;

if (o.hmode && isNaN(parseInt(o.root.style.left ))) o.root.style.left = "0px";
if (o.vmode && isNaN(parseInt(o.root.style.top ))) o.root.style.top = "0px";
if (!o.hmode && isNaN(parseInt(o.root.style.right ))) o.root.style.right = "0px";
if (!o.vmode && isNaN(parseInt(o.root.style.bottom))) o.root.style.bottom = "0px";

o.minX = typeof minX != 'undefined' ? minX : null;
o.minY = typeof minY != 'undefined' ? minY : null;
o.maxX = typeof maxX != 'undefined' ? maxX : null;
o.maxY = typeof maxY != 'undefined' ? maxY : null;

o.xMapper = fXMapper ? fXMapper : null;
o.yMapper = fYMapper ? fYMapper : null;

o.root.onDragStart = new Function();
o.root.onDragEnd = new Function();
o.root.onDrag = new Function();
},

start : function(e)
{
var o = Drag.obj = this;
e = Drag.fixE(e);
var y = parseInt(o.vmode ? o.root.style.top : o.root.style.bottom);
var x = parseInt(o.hmode ? o.root.style.left : o.root.style.right );
o.root.onDragStart(x, y);

o.lastMouseX = e.clientX;
o.lastMouseY = e.clientY;

if (o.hmode) {
if (o.minX != null) o.minMouseX = e.clientX - x + o.minX;
if (o.maxX != null) o.maxMouseX = o.minMouseX + o.maxX - o.minX;
} else {
if (o.minX != null) o.maxMouseX = -o.minX + e.clientX + x;
if (o.maxX != null) o.minMouseX = -o.maxX + e.clientX + x;
}

if (o.vmode) {
if (o.minY != null) o.minMouseY = e.clientY - y + o.minY;
if (o.maxY != null) o.maxMouseY = o.minMouseY + o.maxY - o.minY;
} else {
if (o.minY != null) o.maxMouseY = -o.minY + e.clientY + y;
if (o.maxY != null) o.minMouseY = -o.maxY + e.clientY + y;
}

document.onmousemove = Drag.drag;
document.onmouseup = Drag.end;

return false;
},

drag : function(e)
{
e = Drag.fixE(e);
var o = Drag.obj;

var ey = e.clientY;
var ex = e.clientX;
var y = parseInt(o.vmode ? o.root.style.top : o.root.style.bottom);
var x = parseInt(o.hmode ? o.root.style.left : o.root.style.right );
var nx, ny;

if (o.minX != null) ex = o.hmode ? Math.max(ex, o.minMouseX) : Math.min(ex, o.maxMouseX);
if (o.maxX != null) ex = o.hmode ? Math.min(ex, o.maxMouseX) : Math.max(ex, o.minMouseX);
if (o.minY != null) ey = o.vmode ? Math.max(ey, o.minMouseY) : Math.min(ey, o.maxMouseY);
if (o.maxY != null) ey = o.vmode ? Math.min(ey, o.maxMouseY) : Math.max(ey, o.minMouseY);

nx = x + ((ex - o.lastMouseX) * (o.hmode ? 1 : -1));
ny = y + ((ey - o.lastMouseY) * (o.vmode ? 1 : -1));

if (o.xMapper) nx = o.xMapper(y)
else if (o.yMapper) ny = o.yMapper(x)

Drag.obj.root.style[o.hmode ? "left" : "right"] = nx + "px";
Drag.obj.root.style[o.vmode ? "top" : "bottom"] = ny + "px";
Drag.obj.lastMouseX = ex;
Drag.obj.lastMouseY = ey;

Drag.obj.root.onDrag(nx, ny);
return false;
},

end : function()
{
document.onmousemove = null;
document.onmouseup = null;
Drag.obj.root.onDragEnd( parseInt(Drag.obj.root.style[Drag.obj.hmode ? "left" : "right"]),
parseInt(Drag.obj.root.style[Drag.obj.vmode ? "top" : "bottom"]));
Drag.obj = null;
},

fixE : function(e)
{
if (typeof e == 'undefined') e = window.event;
if (typeof e.layerX == 'undefined') e.layerX = e.offsetX;
if (typeof e.layerY == 'undefined') e.layerY = e.offsetY;
return e;
}
};

二：拖拽排序也是一种常见的效果

常见实现思路

1.将点击进行拖拽的元素转换为绝对路径，同时新建一个临时元素替代其所在的位置。

2.移动过程中通过循环计算鼠标与剩余元素的位置关系，如果鼠标位置处于该元素中时，在该元素的nextSibling前面插入第1步时创建的临时元素；

3.结束时在临时元素前面插入被拖拽元素，删除临时元素。

网上有个冷月无声博主写的挺好的，在此转载一下其代码

以下为其代码
复制代码 代码如下:
(function(win, doc){
var _this = null;
var info = {};
var list = [];
var Sortable = function(opts) {
this.opts = opts;
_this = this;
list = X.getByClass(this.opts.sortClass, doc);
X.addEvent(doc, 'mousedown', this.handleEvent);
X.addEvent(doc, 'mousemove', this.handleEvent);
X.addEvent(doc, 'mouseup', this.handleEvent);
};
Sortable.prototype = {
handleEvent: function(event) {
var e = event || win.event;
var target = event.target || event.srcElement;
switch (event.type) {
case 'mousedown':
X.hasClass(target, _this.opts.sortClass) && _this.downEvent.call(_this, e, target);
break;
case 'mousemove':
info.dObj && _this.moveEvent.call(_this, e, target);
break;
case 'mouseup':
info.dObj && _this.upEvent.call(_this, e, target);
break;
default: break;
}
},
downEvent: function(e, target) {
info.dObj = target;
var off = X.getOffset(target);
target.x = e.clientX - off[0];
target.y = e.clientY - off[1];
target.style.position = 'absolute';
target.style.left = off[0] +'px';
target.style.top = off[1] +'px';

info.vObj = doc.createElement('div');
info.vObj.style.width = off[2] +'px';
info.vObj.style.height = off[3] +'px';
target.parentNode.insertBefore(info.vObj, target);
},
moveEvent: function(e, target) {
win.getSelection ? win.getSelection().removeAllRanges() : doc.selection.empty();
info.dObj.style.left = e.clientX - info.dObj.x +'px';
info.dObj.style.top = e.clientY - info.dObj.y +'px';
for(var i = 0; i < list.length; i++) {
if(list[i] === info.dObj) {
continue;
}
var off = X.getOffset(list[i]);
if(e.clientX > off[0] && e.clientX < off[0] + off[2] && e.clientY > off[1] && e.clientY < off[1] + off[3]) {
switch (true) {
case e.clientY < (off[1] + off[3]) / 2:
list[i].parentNode.insertBefore(info.vObj, list[i]);
break;
case !list[i].nextSibling:
list[i].parentNode.appendChild(info.vObj);
break;
default:
list[i].parentNode.insertBefore(info.vObj, list[i].nextSibling);
break;
}
}
}
},
upEvent: function(e, target) {
info.dObj.style.position = 'static';
info.vObj.parentNode.insertBefore(info.dObj, info.vObj);
info.dObj.parentNode.removeChild(info.vObj);
info = {};
}
};
win.Sortable = Sortable;
})(window, document);