js拖拽的常見思路
1.通過onmousedown,onmousemove,onmouseup分別模擬開始拖拽，拖拽中和拖拽結束時的事件（）。
如果手機的觸摸事件的話則分別是ontouchstart,ontouchmove和ontouchend。
2.鼠標按下即發生onmousedown事件時：獲取鼠標位置，獲取被拖動元素的位置，記錄兩者之間的縱橫坐標的差值（）。對document元素綁定onmousemove,onmouseup事件。
剛開始接觸js拖拽時，我當時疑惑的是為什麼是對document綁定而不是對被拖動的元素綁定呢？原來是如果對被拖動元素綁定的話當鼠標拖動過快時，會導致鼠標與被拖動元素的脫離。
3.鼠標拖動即發生onmousemove事件時：將被拖拽元素的position改成絕對位置，這個可以通過left和top改變該元素的位置，從而使得該元素隨著鼠標的拖拽而移動。獲取鼠標位置，將鼠標x坐標（e.clientX）減去第2步儲存的橫坐標差作為被拖動元素的left值，將鼠標x坐標（e.clientY）減去第2步儲存的縱坐標差作為被拖動元素的top值。實現元素跟隨鼠標拖動的效果。
4.鼠標按鍵彈起即發生onmouseup事件時：清空onmousemove和onmouseup事件
比較流行的拖拽插件dom-drag類庫（作者： Aaron Boodman）
其源代碼如下
複製代碼代碼如下:
/*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：拖拽排序也是一種常見的效果
常見實現思路
1.將點擊進行拖拽的元素轉換為絕對路徑，同時新建一個臨時元素替代其所在的位置。
2.移動過程中通過循環計算鼠標與剩餘元素的位置關係，如果鼠標位置處於該元素中時，在該元素的nextSibling前面插入第1步時創建的臨時元素；
3.結束時在臨時元素前面插入被拖拽元素，刪除臨時元素。
網上有個冷月無聲博主寫的挺好的，在此轉載一下其代碼
以下為其代碼
複製代碼代碼如下:
(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);