parseFloat rounding

Question

I have javascript function that automatically adds input fields together, but adding numbers like 1.35 + 1.35 + 1.35 gives me an output of 4.050000000000001, just as an exam

Answer 1

You can use Math.round(total*100000000000)/100000000000; in the code. It will work for most of the cases

Answer 2

Instead of rounding, you may want to use the port of Java's BigDecimal to get actually precise decimal math.

Answer 3

This works:

$(document).ready(
    function() {
            $('#field1').blur(function(){ $('#field2').val(parseFloat($(this).val() * 2.2).toFixed(1)); });
            $('#field2').blur(function(){ $('#field1').val(parseFloat($(this).val() / 2.2).toFixed(1)); });
    }
);

This fails:

$(document).ready(
    function() {
            $('#field1').blur(function(){ $('#field2').val(parseFloat($(this).val() * 2.2)).toFixed(1); });
            $('#field2').blur(function(){ $('#field1').val(parseFloat($(this).val() / 2.2)).toFixed(1); });
    }
);

So be careful the way you place your parenthesis ()... In first case, the rounding will work, but won't work in the second one...

Answer 4

Use toFixed() to round num to 2 decimal digits using the traditional rounding method. It will round 4.050000000000001 to 4.05.

num.toFixed(2);

You might prefer using toPrecision(), which will strip any resulting trailing zeros.

Example:

1.35+1.35+1.35 => 4.050000000000001
(1.35+1.35+1.35).toFixed(2)     => 4.05
(1.35+1.35+1.35).toPrecision(3) => 4.05

// or...
(1.35+1.35+1.35).toFixed(4)     => 4.0500
(1.35+1.35+1.35).toPrecision(4) => 4.05

Reference: JavaScript Number Format - Decimal Precision

Answer 5

var num = 4.050000000000001;

num = num.toFixed(2);

toFixed will round up depending on how many digits after the decimal you're looking for.