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<decimals-decs;i++) newString += "0";
	//var newNumber = Number(newString);// make it a number if you like
	document.roundform.roundedfield.value = newString; // Output the result to the form field (change for your purposes)
}

 

 

 

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