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
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
