Js setInterval 定时器

var myTimer;
var speed = 100; //速度毫秒 值越小速度越快
var stepSpeed = 4; //值越大越快
$(function() {
var mybox = $(".scroll_box");
//向上
$(".scroll_up").bind("mouseover", function() {
var nowPos = mybox[boxCount].scrollTop; //当前值
changePos(mybox, nowPos, 0);
}).bind("mouseout", function() {
if (myTimer) { window.clearInterval(myTimer); }
});
//向下
$(".scroll_down").bind("mouseover", function() {
var nowPos = mybox[boxCount].scrollTop; //当前值
var maxPos = mybox[boxCount].scrollHeight - mybox.outerHeight(); //最大值
changePos(mybox, nowPos, maxPos);
}).bind("mouseout", function() {
if (myTimer) { window.clearInterval(myTimer); }
});
});

function changePos(box, from, to) {
if (myTimer) { window.clearInterval(myTimer); }
var temStepSpeed = stepSpeed;
if (from > to) {
myTimer = window.setInterval(function() {
if (box[boxCount].scrollTop > to) { box[boxCount].scrollTop -= (5 + temStepSpeed); temStepSpeed += temStepSpeed; }
else { window.clearInterval(myTimer); }
}, speed);
} else if (from < to) {
myTimer = window.setInterval(function() {
if (box[boxCount].scrollTop < to) { box[boxCount].scrollTop += (5 + temStepSpeed); temStepSpeed += temStepSpeed; }
else { window.clearInterval(myTimer); }
}, speed);
}
}