day20-21/task6.html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Day20-21</title>
  <style>
    #erikface {
      margin: 0 auto;
      width: 480px;
      height: 480px;
      background-color: #ccc;
      background-image: url(erik_smile.jpg);
      background-repeat: no-repeat;
      background-position: 0 -480px;
    }
  </style>
</head>
<body>
  <div id="erikface"></div>
</body>

<script type="text/javascript">
    var erikface,
        faceHeight,
        pattern,    // inc or dec;
        yVal,
        i;

    erikface = document.querySelector("#erikface");
    faceHeight = parseInt(window.getComputedStyle(erikface, null).height);
    pattern = 0;
    yVal = 0;
    function changeBgPos(miny, maxy) {
        if (pattern === 1) {
            yVal += faceHeight;
        } else if (pattern === 0) {
            yVal -= faceHeight;
        }

        if (yVal === miny) {
            pattern = 1;
        }
        if (yVal === maxy) {
            pattern = 0;
        }
        // console.log(yVal);
        erikface.style.backgroundPosition = "0 " + yVal +"px";
    }
    setInterval(changeBgPos, 100, -16*faceHeight, 0);
</script>
</html>