在開發過程中經常遇到要調整小數的格式，如保留小數點後兩位等等。方法也頗為常見，備忘如下。
第一種，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
第二種，js1.5以上可以利用toFixed(x) ，可指定數字截取小數點後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
以上兩種方法最通用，但卻無法滿足某些特殊要求，比如保留小數點後兩位，如果不滿兩位，不滿兩位則補零。此時就有了第三種方法。
第三種，轉換函數，這段代碼來源於國外一個論壇。
複製代碼代碼如下:
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