根据动画原理，初步封装运动函数 2_封装运动函数的理论步骤-优快云博客

本文链接：https://blog.youkuaiyun.com/stopcpp/article/details/52861201

<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        #box{
            width: 100px;
            height: 100px;
            background-color: pink;
            position: absolute;
        }
    </style>
</head>
<body>
    <button id="btn200">200</button>
    <button id="btn400">400</button>
    <div id="box"></div>
</body>
</html>
<script>
    var box = document.getElementById("box");
    var btn200 = document.getElementById("btn200");
    var btn400 = document.getElementById("btn400");
    btn200.onclick = function () {
        animate(box,200);
    }
    btn400.onclick = function () {
        animate(box,400);
    }
    function animate(obj,target){
        clearInterval(obj.timer);
        var speed = obj.offsetLeft < target ? 5 : -5; //用来判断是+还是-
        obj.timer = setInterval(function(){
            var result = target - obj.offsetLeft;  //因为目标位置与offsetLeft差值不会超过5
            obj.style.left = obj.offsetLeft + speed + "px";
            if(Math.abs(result) <= 5){  //如果差值少于5，说明到位置了。
                clearInterval(obj.timer);
                obj.style.left = target + "px";  //有最多5像素的差距，就直接跳转到target位置。
            }
        },30);
    }
</script>