JavaScript保留小数点后指定位数的方法详解

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
 

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 != ".") {  //www.jiaochengji.com
                        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