function moveElement(elementID,final_x,final_y,interval) {
if (!document.getElementById) return false;
//???
if (!document.getElementById(elementID)) return false;
//如果找不到elementId 的元素 那么返回 false;
var elem = document.getElementById(elementID);
//得到 elementId 的元素
if (elem.movement) {
clearTimeout(elem.movement);
}
if (!elem.style.left) {
elem.style.left = "0px";
}
if (!elem.style.top) {
elem.style.top = "0px";
}
var xpos = parseInt(elem.style.left);
var ypos = parseInt(elem.style.top);
if (xpos == final_x && ypos == final_y) {
moveing = false; //?????
return true;
}
if (xpos < final_x) {
var dist = Math.ceil((final_x - xpos)/10);
xpos = xpos + dist;
}
if (xpos > final_x) {
var dist = Math.ceil((xpos - final_x)/10);
xpos = xpos - dist;
}
if (ypos < final_y) {
var dist = Math.ceil((final_y - ypos)/10);
ypos = ypos + dist;
}
if (ypos > final_y) {
var dist = Math.ceil((ypos - final_y)/10);
ypos = ypos - dist;
}
elem.style.left = xpos + "px";
elem.style.top = ypos + "px";
var repeat = "moveElement('"+elementID+"',"+final_x+","+final_y+","+interval+")";
elem.movement = setTimeout(repeat,interval);
}解释一下这段代码,有几个地方看不大懂
1 . if (elem.movement) {
clearTimeout(elem.movement);
}
2.if (!elem.style.left) {
elem.style.left = "0px";
}
3.moveing = false; //?????
4.var dist = Math.ceil((final_x - xpos)/10);这个函数是用来干嘛的?
clearTimeout(elem.movement);
}
如果正在运动,就清除运动函数,重新开始运动。------------------------------------------------
2.if (!elem.style.left) {
elem.style.left = "0px";
}
如果left为0 , false 或者 null , 则置为 0px
------------------------------------------------
3.moveing = false; //?????正在移动的标志设为false
这个变量其他地方应该有用到------------------------------------------------
4.var dist = Math.ceil((final_x - xpos)/10);这个函数是用来干嘛的? 计算距离
Math.ceil()是向上取整的函数
var ypos = parseInt(elem.style.top);
if (xpos == final_x && ypos == final_y) {
moveing = false; //?????
return true;
}
if (xpos < final_x) {
var dist = Math.ceil((final_x - xpos)/10);
xpos = xpos + dist;
}
if (xpos > final_x) {
var dist = Math.ceil((xpos - final_x)/10);
xpos = xpos - dist;
}
if (ypos < final_y) {
var dist = Math.ceil((final_y - ypos)/10);
ypos = ypos + dist;
}
if (ypos > final_y) {
var dist = Math.ceil((ypos - final_y)/10);
ypos = ypos - dist;
}为什么要这么写呢?