js javascrip 截取小數點後幾位

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。方法也頗爲常見，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。

 

 

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