js拖动

gistfile1.js

window.onload = function () {
    drag(document.getElementById('drag'), [200, 400, 30, 300]);
};

function drag(o, r) {
    o.firstChild.onmousedown = function () {
        return false;
    };
    o.onmousedown = function (a) {
        o.style.cursor = 'move';
        var d = document;
        if (!a) a = window.event;
        var x = a.layerX ? a.layerX : a.offsetX,
            y = a.layerY ? a.layerY : a.offsetY;
        if (o.setCapture) o.setCapture();
        else if (window.captureEvents) window.captureEvents(Event.MOUSEMOVE | Event.MOUSEUP);
        d.onmousemove = function (a) {
            if (!a) a = window.event;
            if (!a.pageX) a.pageX = a.clientX;
            if (!a.pageY) a.pageY = a.clientY;
            var tx = a.pageX - x,
                ty = a.pageY - y;
            o.style.left = tx < r[0] ? r[0] : tx > r[1] ? r[1] : tx;
            o.style.top = ty < r[2] ? r[2] : ty > r[3] ? r[3] : ty;
        };
        d.onmouseup = function () {
            if (o.releaseCapture) o.releaseCapture();
            else if (window.captureEvents) window.captureEvents(Event.MOUSEMOVE | Event.MOUSEUP);
            d.onmousemove = null;
            d.onmouseup = null;
            o.style.cursor = '';
        };
    };
}