JS保留小数几种简单方法例子

var num = 1
num = num.toFixed(1)   
console.log(num);   //1.0

var num = 1.55
var num1 = 1.45          //5前为偶舍去
num1 = num1.toFixed(1)
num = num.toFixed(1)   
console.log(num);   //1.6
console.log(num1);  //1.4

function roundFun(value, n) {
  return Math.round(value*Math.pow(10,n))/Math.pow(10,n);
}
console.log(roundFun(2.853，2));  //2.85
console.log(roundFun(5/3, 2)     //1.67
console.log(roundFun(2, 2)       //2      

//输入小数value，并保留小数点后一位，如果想保留两位，将10改为100
function roundFun(value) {
    return Math.round(value * 10) / 10;
}
console.log(roundFun(2.853));      //2.9

//保留n位小数并格式化输出（不足的部分补0）
    function fomatFloat(value, n) {
      var f = Math.round(value * Math.pow(10, n)) / Math.pow(10, n);
      var s = f.toString();
      var rs = s.indexOf(".");
      if (rs < 0) {
        s += ".";
      }
      for (var i = s.length - s.indexOf("."); i <= n; i++) {
        s += "0";
      }
      return s;
    };
    console.log(fomatFloat(1,2));    //1.00

Math.round(xx) // 参数 ‘xx' 代表一个数值  

var xx= 20.5;
console.log(Math.round(xx, xx)) // 21

var xx= 20.49;
console.log(Math.round(xx)) // 20

var xx= -20.5;
var xx= -20.55;
console.log(Math.round(xx)) // -20
console.log(Math.round(xx)) // -21