| 1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859 | <!DOCTYPE html><html lang="en"><head>  <meta charset="UTF-8">  <meta http-equiv="X-UA-Compatible" content="IE=edge">  <meta name="viewport" content="width=device-width, initial-scale=1.0">  <title>Document</title>  <style>    * {      margin: 0;      padding: 0;    }    #div1 {      width: 200px;      height: 200px;      background: red;      transition: width 2s linear;    }  </style></head><body>  <button id="up">放大</button>  <div id="div1"></div>  <button id="down">缩小</button>  <script>    var up = document.getElementById('up')    var down = document.getElementById('down')    var div1 = document.getElementById('div1')    // up.onclick = function () {    //   var timer = setInterval(function () {    //     if (div1.offsetWidth < 500) {    //       div1.style.width = div1.offsetWidth + 10 + 'px'    //     } else {    //       clearInterval(timer)    //     }    //   }, 10);    //   // div1.style.width = 500 + 'px'    // }    up.onclick = function () {      div1.style.width = 500 + 'px'    }    down.onclick = function () {      var timer1 = setInterval(function () {        if (div1.offsetWidth > 0) {          div1.style.width = div1.offsetWidth - 10 + 'px'        } else {          clearInterval(timer1)        }      }, 10)    }  </script></body></html>
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