JavaScript之保留小数点后指定位数

在开发过程中经常遇到要调整小数的格式，如保留小数点后两位等等。方法也颇为常见，备忘如下。

第一种，利用math.round

var original=28.453
1) //round "original" to two decimals
var result=Math.round(original*100)/100; //returns 28.45
2) // round "original" to 1 decimal
var result=Math.round(original*10)/10; //returns 28.5

第二种，js1.5以上可以利用toFixed(x) ，可指定数字截取小数点后 x位

3) //round "original" to two decimals
var result=original.toFixed(2);//returns 28.45

4) // round "original" to 1 decimal
var result=original.toFixed(1); //returns 28.5

以上两种方法最通用，但却无法满足某些特殊要求，比如保留小数点后两位，如果不满两位，不满两位则补零。此时就有了第三种方法。

第三种，转换函数，这段代码来源于国外一个论坛。

function roundNumber(number,decimals) { var newString;// The new rounded number decimals = Number(decimals); if (decimals < 1) { newString = (Math.round(number)).toString(); } else { var numString = number.toString(); if (numString.lastIndexOf(".") == -1) {// If there is no decimal point numString += ".";// give it one at the end } var cutoff = numString.lastIndexOf(".") + decimals;// The point at which to truncate the number var d1 = Number(numString.substring(cutoff,cutoff+1));// The value of the last decimal place that we'll end up with var d2 = Number(numString.substring(cutoff+1,cutoff+2));// The next decimal, after the last one we want if (d2 >= 5) {// Do we need to round up at all? If not, the string will just be truncated if (d1 == 9 && cutoff > 0) {// If the last digit is 9, find a new cutoff point while (cutoff > 0 && (d1 == 9 || isNaN(d1))) { if (d1 != ".") { cutoff -= 1; d1 = Number(numString.substring(cutoff,cutoff+1)); } else { cutoff -= 1; } } } d1 += 1; } if (d1 == 10) { numString = numString.substring(0, numString.lastIndexOf(".")); var roundedNum = Number(numString) + 1; newString = roundedNum.toString() + '.'; } else { newString = numString.substring(0,cutoff) + d1.toString(); } } if (newString.lastIndexOf(".") == -1) {// Do this again, to the new string newString += "."; } var decs = (newString.substring(newString.lastIndexOf(".")+1)).length; for(var i=0;i

5) //round "original" to two decimals
var result=original.toFixed(2);//returns 28.45

6) // round "original" to 1 decimal
var result=original.toFixed(1); //returns 28.5

var original=28.4

var result=original.toFixed(2);//returns 28.40