JavaScript保留两位小数的多种实现方案与类型差异解析

 var num =2.446242342;  
 num = num.toFixed(2); 
 console.log(num); //2.45
 console.log(typeof num); // string

num = Math.floor(num * 100) / 100;
console.log(num); //2.44
console.log(typeof num); // number

num = Number(num.toString().match(/^\d+(?:\.\d{0,2})?/));
console.log(num); //2.44
console.log(typeof num); // number

function keepTwoDecimal(num) {
   var result = parseFloat(num);
   if (isNaN(result)) {
       alert('传递参数错误，请检查！');
       return false;
   }
   result = Math.round(num * 100) / 100;
   return result;
};
 keepTwoDecimal(num);
 console.log(num); //2.44
 console.log(typeof num); //number

function keepTwoDecimalFull(num) {
  var result = parseFloat(num);
  if (isNaN(result)) {
      alert('传递参数错误，请检查！');
      return false;
  }
  result = Math.round(num * 100) / 100;
  var s_x = result.toString(); //将数字转换为字符串
  var pos_decimal = s_x.indexOf('.'); //小数点的索引值
  // 当整数时，pos_decimal=-1 自动补0
  if (pos_decimal < 0) {
      pos_decimal = s_x.length;
      s_x += '.';
  }
  // 当数字的长度< 小数点索引+2时，补0
  while (s_x.length <= pos_decimal + 2) {
      s_x += '0';
  }
  return s_x;
}
 console.log(keepTwoDecimalFull(120.5)); //120.50
 console.log(typeof keepTwoDecimalFull(120.5)); //string
 console.log(keepTwoDecimalFull(2.446242342)); //2.45
 console.log(typeof keepTwoDecimalFull(2.446242342)); //string

function toDecimal(x) {
 var f = parseFloat(x);
 if (isNaN(f)) {
  return;
 }
 f = Math.round(x*100)/100;
 return f;
}
console.log(toDecimal(3.1465926)); // 3.15
console.log(typeof toDecimal(3.1415926)); //number

function toDecimal2(x) {
 var f = parseFloat(x);
 if (isNaN(f)) {
  return false;
 }
 var f = Math.round(x*100)/100;
 var s = f.toString();
 var rs = s.indexOf('.');
 if (rs < 0) {
  rs = s.length;
  s += '.';
 }
 while (s.length <= rs + 2) {
  s += '0';
 }
 return s;
}
console.log(toDecimal2(3.1)); // 3.10
console.log(typeof toDecimal2(3.1415926)); //string

function fomatFloat(src,pos){
  return Math.round(src*Math.pow(10, pos))/Math.pow(10, pos);
}
 console.log(fomatFloat(3.12645,2)); // 3.13
console.log(typeof fomatFloat(3.1415926)); //number