<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>

​