JavaScript之保留小数点后指定位数

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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

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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.var result=original.function roundNumber(number,decimals) {var newString;// The new rounded numberdecimals = Number(decimals);if (decimals < 1) {newString = (Math.round(number)).toString();} else {var numString = number.toString();if (numString.lastIndexOf(".") == -1) {// If there is no decimal pointnumString += ".";// give it one at the end}var cutoff = numString.lastIndexOf(".") + decimals;// The point at which to truncate the numbervar d1 = Number(numString.substring(cutoff,cutoff+1));// The value of the last decimal place that we'll end up withvar d2 = Number(numString.substring(cutoff+1,cutoff+2));// The next decimal, after the last one we wantif (d2 >= 5) {// Do we need to round up at all? If not, the string will just be truncatedif (d1 == 9 && cutoff > 0) {// If the last digit is 9, find a new cutoff pointwhile (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 stringnewString += ".";}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 likedocument.roundform.roundedfield.value = newString; // Output the result to the form field (change for your purposes)}

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5) //round "original" to two decimals

var result=original.var result=original.toFixed(1); //returns 28.5

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var original=28.4

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

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