JS 控制图片的淡进淡出

<script>
var speed = 50; //速度
var max_opacity = 100; //最大
var min_opacity = 10; //最小
var do_step = 5; //变化的幅度

function change_opacity(obj,do_option)
{
if(obj.doing)
clearInterval(obj.doing);
obj.doing = setInterval(do_option+"_alpha("+obj.sourceIndex+")",speed);
}

function down_alpha(obj_index)
{
var obj = document.all[obj_index];

if(obj.filters.Alpha.Opacity > min_opacity )
{
obj.filters.Alpha.Opacity += -do_step;
}
else
{
clearInterval(obj.doing);
obj.filters.Alpha.Opacity = min_opacity;
obj.doing = false;
}
}
function up_alpha(obj_index)
{
var obj = document.all[obj_index];

if(obj.filters.Alpha.Opacity<max_opacity)
obj.filters.Alpha.Opacity += do_step;
else
{
clearInterval(obj.doing);
obj.filters.Alpha.Opacity = max_opacity;
obj.doing = false;
}
}

</script>

下面是调用. 适合图片.文字我还没有测试.

tyle="cursor:pointer;filter:Alpha(Opacity=10)"

onMouseOver="change_opacity(this,'up')"

onMouseOut="change_opacity(this,'down')"