效果一：

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>demo</title>
</head>
<body>
    <button id="btn">走你</button>
    <button id="btn2">回来</button>

<script type="text/javascript">
    var div = document.createElement('div');
    document.body.appendChild(div);
    div.style.width = "100px";
    div.style.height = "100px";
    div.style.background = "red";
    div.style.position = "absolute";
    div.style.left =  "0px";
    div.style.top = "50px";

    //走你按钮触发事件
    document.getElementById('btn').onclick = function(){
        var timeId = setInterval(function(){
            div.style.left = parseInt(div.style.left) + 5  + "px";
            if (div.style.left=='400px') {
                clearInterval(timeId);
            }
        },50);
    }

    //回来按钮触发事件
    document.getElementById('btn2').onclick = function(){
    var timeId = setInterval(function(){
        div.style.left = parseInt(div.style.left) - 5  + "px";
        if (div.style.left=='0px') {
            clearInterval(timeId);
        }
    },50);
}

</script>
</body>
</html>

 

两个div 封装：

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>document</title>
</head>
<style type="text/css">
    * {
        margin: 0;
        padding: 0;
    }

    .box {
        width: 200px;
        height: 200px;
        background: slateblue;
        position: relative;
    }

    .box2 {
        width: 200px;
        height: 200px;
        background: pink;
        position: relative;
    }
</style>
<body>

    <button>走你</button>
    <button id="back">后退</button>
    
    <div class="box"></div>
    <div class="box2"></div>

</body>
<script type="text/javascript">
    var btn = document.getElementsByTagName('button')[0];
    var box = document.getElementsByClassName('box')[0];
    var box2 = document.getElementsByClassName('box2')[0];
    var btn2 = document.getElementById('back');
    var timer;

    btn.onclick = function(){
        /*动画的公式
            leader = leader + step
            元素的自身位置 = 元素位置 + 每次移动的速度
        */
        
        animate(box,300);
        animate(box2,600);    
    }

    btn2.onclick = function(){
        //alert('111');
        animate(box,0);
        animate(box2,0);
    }

    // 封装
    function animate(obj,distance){

        obj.timer = setInterval(function(){
            var leader = obj.offsetLeft;
            console.log(leader);
            var step = 10;
            console.log(step);

            step = leader>distance?-step:step;

            leader == distance?clearInterval(obj.timer):obj.style.left = leader + step + "px";

            },16);

    }

</script>
</html>