var x = 0.3445434
x = Math.round (x*100) / 100 // this will make nice rounding

也许你还需要小数分隔符?这是我刚刚创建的一个函数:

function formatFloat(num,casasDec,sepDecimal,sepMilhar) {
    if (num < 0)
    {
        num = -num;
        sinal = -1;
    } else
        sinal = 1;
    var resposta = "";
    var part = "";
    if (num != Math.floor(num)) // decimal values present
    {
        part = Math.round((num-Math.floor(num))*Math.pow(10,casasDec)).toString(); // transforms decimal part into integer (rounded)
        while (part.length < casasDec)
            part = '0'+part;
        if (casasDec > 0)
        {
            resposta = sepDecimal+part;
            num = Math.floor(num);
        } else
            num = Math.round(num);
    } // end of decimal part
    while (num > 0) // integer part
    {
        part = (num - Math.floor(num/1000)*1000).toString(); // part = three less significant digits
        num = Math.floor(num/1000);
        if (num > 0)
            while (part.length < 3) // 123.023.123  if sepMilhar = '.'
                part = '0'+part; // 023
        resposta = part+resposta;
        if (num > 0)
            resposta = sepMilhar+resposta;
    }
    if (sinal < 0)
        resposta = '-'+resposta;
    return resposta;
}

我认为这里的关键是首先正确地舍入，然后您可以将其转换为String。

function roundOf(n, p) {
    const n1 = n * Math.pow(10, p + 1);
    const n2 = Math.floor(n1 / 10);
    if (n1 >= (n2 * 10 + 5)) {
        return (n2 + 1) / Math.pow(10, p);
    }
    return n2 / Math.pow(10, p);
}

// All edge cases listed in this thread
roundOf(95.345, 2); // 95.35
roundOf(95.344, 2); // 95.34
roundOf(5.0364342423, 2); // 5.04
roundOf(0.595, 2); // 0.60
roundOf(0.335, 2); // 0.34
roundOf(0.345, 2); // 0.35
roundOf(551.175, 2); // 551.18
roundOf(0.3445434, 2); // 0.34

现在可以使用toFixed(p)安全地格式化这个值。 在你的具体案例中

roundOf(0.3445434, 2).toFixed(2); // 0.34

There is no way to avoid inconsistent rounding for prices with x.xx5 as actual value using either multiplication or division. If you need to calculate correct prices client-side you should keep all amounts in cents. This is due to the nature of the internal representation of numeric values in JavaScript. Notice that Excel suffers from the same problems so most people wouldn't notice the small errors caused by this phenomen. However errors may accumulate whenever you add up a lot of calculated values, there is a whole theory around this involving the order of calculations and other methods to minimize the error in the final result. To emphasize on the problems with decimal values, please note that 0.1 + 0.2 is not exactly equal to 0.3 in JavaScript, while 1 + 2 is equal to 3.

/** don't spend 5 minutes, use my code **/
function prettyFloat(x,nbDec) { 
    if (!nbDec) nbDec = 100;
    var a = Math.abs(x);
    var e = Math.floor(a);
    var d = Math.round((a-e)*nbDec); if (d == nbDec) { d=0; e++; }
    var signStr = (x<0) ? "-" : " ";
    var decStr = d.toString(); var tmp = 10; while(tmp<nbDec && d*tmp < nbDec) {decStr = "0"+decStr; tmp*=10;}
    var eStr = e.toString();
    return signStr+eStr+"."+decStr;
}

prettyFloat(0);      //  "0.00"
prettyFloat(-1);     // "-1.00"
prettyFloat(-0.999); // "-1.00"
prettyFloat(0.5);    //  "0.50"

有一些函数可以取整数字。例如:

var x = 5.0364342423;
print(x.toFixed(2));

将打印5.04。

编辑: 小提琴