Math account with exact precision returns different value in Javascript

Question

I have the following mathematical operation, and what’s worse, this operation manipulates monetary values.

3898.95 / 3.0

If you do this operation on the calculator the result will be equal to: 1299,65 exact.

But with Javascript the result will be equal to: 1299,649999999999, just put this operation on an Alert that you will see the result.

And in my application only accepts 2 decimal numbers after the comma and truncates the rest with the use of a filter in Angularjs, ie in a installment will always lack a few cents since the result will be 1299,64.

Filter in Angularjs:

app.filter("currencyRounded",function(){    
    return function(val){
        return truncateDecimals(val, 2);
    }
});

Functions that filter execution calls:

function truncateDecimals (num, digits) {
    if (num == undefined) num = 0.0;
    var numS = num.toString(),
        decPos = numS.indexOf('.'),
        substrLength = decPos == -1 ? numS.length : 1 + decPos + digits,
        trimmedResult = numS.substr(0, substrLength),
        finalResult = isNaN(trimmedResult) ? 0 : trimmedResult;

    return formatOnlyNumber(parseFloat(finalResult)).replace(/\./g,',');
}

function formatOnlyNumber(valor){
    return parseFloat(Math.round(valor * 100) / 100).toFixed(2);
}

But the main question is, how to have 1299,65 as a result? If you are only using Javascript without any other better function yet.

Answer 1

Multiply its value by 100, making its decimals into integers. Round using the Math.round(), eliminating the decimals, and divide the result by 100, recovering the decimals.

console.log(Math.round(1299.649999999999 * 100) / 100);

You can also choose to use Math.floor() (rounding down) or the Math.ceil() (rounding up).

Answer 2

    Number.prototype.formatMoney = function(c, d, t){
var n = this, 
    c = isNaN(c = Math.abs(c)) ? 2 : c, 
    d = d == undefined ? "." : d, 
    t = t == undefined ? "," : t, 
    s = n < 0 ? "-" : "", 
    i = parseInt(n = Math.abs(+n || 0).toFixed(c)) + "", 
    j = (j = i.length) > 3 ? j % 3 : 0;
   return s + (j ? i.substr(0, j) + t : "") + i.substr(j).replace(/(\d{3})(?=\d)/g, "$1" + t) + (c ? d + Math.abs(n - i).toFixed(c).slice(2) : "");
 };


new Number(3898.95 / 3.0 ).formatMoney(2,',','.');

Even though I marked it as duplicate myself, but maybe you didn’t understand how to use the function, so ta ai.

/a/11267/12032