javascript 保留小数点后N为

// 保留小数点后N位
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
	return newString; // Output the result to the form field (change for your purposes)
}

//use：roundNumber('113.2969333',2);
//return:113.30