把数字格式化为指定的长度

<p id="demo">单击按钮来显示格式化的数字。</p>

<button onclick="myFunction()">点我</button>

<script>

  function myFunction() {

    var num = new Number(13.3714);

    var n = num.toPrecision(2);

    var x = document.getElementById("demo");

    x.innerHTML = n

  }

</script>