代码示例:(标识:js_number_toprecision)
<!DOCTYPE html>
<html>
<body>

<h2>JavaScript Number 方法</h2>

<p>toPrecision() 返回字符串,其中包含指定长度的数字:</p>

<p id="demo"></p>

<script>
let x = 9.656;
document.getElementById("demo").innerHTML = 
  x.toPrecision() + "<br>" +
  x.toPrecision(2) + "<br>" +
  x.toPrecision(4) + "<br>" +
  x.toPrecision(6);  
</script>

</body>
</html>
运行结果: