拖动一个HTML元素_javascript技巧

// Demo 0 variables
var DragDrops = [];
var curTarget = null;
var lastTarget = null;

function makeDraggable(item){
if(!item) return;
item.onmousedown = function(ev){
dragObject = this;
mouseOffset = getMouseOffset(this, ev);
return false;
}
}

function getMouseOffset(target, ev){
ev = ev || window.event;

var docPos = getPosition(target);
var mousePos = mouseCoords(ev);
return {x:mousePos.x - docPos.x, y:mousePos.y - docPos.y};
}

function getPosition(e){
var left = 0;
var top = 0;
while (e.offsetParent){
left += e.offsetLeft + (e.currentStyle?(parseInt(e.currentStyle.borderLeftWidth)).NaN0():0);
top += e.offsetTop + (e.currentStyle?(parseInt(e.currentStyle.borderTopWidth)).NaN0():0);
e = e.offsetParent;
}

left += e.offsetLeft + (e.currentStyle?(parseInt(e.currentStyle.borderLeftWidth)).NaN0():0);
top += e.offsetTop + (e.currentStyle?(parseInt(e.currentStyle.borderTopWidth)).NaN0():0);

return {x:left, y:top};

}

function mouseCoords(ev){
if(ev.pageX || ev.pageY){
return {x:ev.pageX, y:ev.pageY};
}
return {
x:ev.clientX + document.body.scrollLeft - document.body.clientLeft,
y:ev.clientY + document.body.scrollTop - document.body.clientTop
};
}

function mouseDown(ev){
ev = ev || window.event;
var target = ev.target || ev.srcElement;

if(target.onmousedown || target.getAttribute('DragObj')){
return false;
}
}

function mouseUp(ev){

//dragObject = null;

if(dragObject){
ev = ev || window.event;
var mousePos = mouseCoords(ev);

var dT = dragObject.getAttribute('droptarget');
if(dT){
var targObj = document.getElementById(dT);
var objPos = getPosition(targObj);
if((mousePos.x > objPos.x) && (mousePos.y > objPos.y)
&& (mousePos.x<(objPos.x+parseInt(targObj.offsetWidth)))
&& (mousePos.y<(objPos.y+parseInt(targObj.offsetHeight)))){
var nSrc = targObj.getAttribute('newSrc');
if(nSrc){
dragObject.src = nSrc;
setTimeout(function(){
if(!dragObject || !dragObject.parentNode) return;
dragObject.parentNode.removeChild(dragObject);
dragObject = null;
}, parseInt(targObj.getAttribute('timeout')));
} else {
dragObject.parentNode.removeChild(dragObject);
}
}
}
}
dragObject = null;

iMouseDown = false;
}

function mouseMove(ev){
ev = ev || window.event;

/*
We are setting target to whatever item the mouse is currently on

Firefox uses event.target here, MSIE uses event.srcElement
*/
var target = ev.target || ev.srcElement;
var mousePos = mouseCoords(ev);

if(dragObject){
dragObject.style.position = 'absolute';
dragObject.style.top = mousePos.y - mouseOffset.y;
dragObject.style.left = mousePos.x - mouseOffset.x;
}

// track the current mouse state so we can compare against it next time
lMouseState = iMouseDown;

// this prevents items on the page from being highlighted while dragging
if(curTarget || dragObject) return false;
}

function addDropTarget(item, target){
item.setAttribute('droptarget', target);
}

document.onmousemove = mouseMove;
document.onmousedown = mouseDown;
document.onmouseup = mouseUp;

window.onload = function (){
makeDraggable(document.getElementById('DragImage9'));
makeDraggable(document.getElementById('DragImage10'));
makeDraggable(document.getElementById('DragImage11'));
makeDraggable(document.getElementById('DragImage12'));

addDropTarget(document.getElementById('DragImage9'), 'TrashImage1');
addDropTarget(document.getElementById('DragImage10'), 'TrashImage1');
addDropTarget(document.getElementById('DragImage11'), 'TrashImage1');
addDropTarget(document.getElementById('DragImage12'), 'TrashImage1');
}

Demo - Drag any of the images