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Home Forums JavaScript .toFixed() probem/issue?

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• #37360
timmey
Member

hey guys,

can someone explain why the hell num2 is correct and num1 isn`t (Firefox, Chome)?

and, if you have it, IE 9 shows the correct numbers?

thanx

#100040
Mottie
Member

Hi Timmey!

Basically the `.toFixed()` rounds off the number. I guess that different browsers handle it differently, so the best solution to just round down would be to just multiply and truncate (demo):

``````var num = new Number(4.725);
var num2 = new Number(4.735);

num = Math.floor( num * 100 ) / 100;
num2 = Math.floor( num2 * 100) / 100;

document.write(num+"");
document.write(num2+"");
``````
#100045
Senff
Participant

But the results of that last demo are not right….

I would expect 4.725 to round off to 4.73, and 4.735 to round off to 4.74.
In the first demo, one is correct and the other one isn’t (I believe that was @timmey ‘s question — why does one round off to the top while the other to the bottom, since both end in 5, in the same browser).
In the second demo, both are incorrect.

#100093
Mottie
Member

I believe it is following the rounding up to the nearest even number rule.

#100094
Senff
Participant

That makes perfect sense, then! :)

#100107
timmey
Member

thx for your response! like senff said, i just wondered why i got differend results.

i found another function that seems to work fine or displays the expected numbers :-) : Your text to link…

#171645
kunjan
Participant

how toFixed is working:

So 0.99 = 1
and 0.98 = 1
and 0.97 = 1
and 0.96 = 1
and 0.95 = 1
and 0.94 = 0.9
and 0.93 = 0.9
and 0.92 = 0.9
and 0.91 = 0.9

the reason is:

When you write “0.95” in normal math, the sequence of characters represents exactly the value 95/100. Rounding that will give 1.

When you write “0.95” to represent a 64-bit double precision number, which is what number literals in JavaScript do, the actual value it represents is 0.94999999999999996, which rounds to 0.9 with one decimal digit.

Double numbers are represented by a fixed number of binary digits, which has the consequence that not all decimal values can be represented – just as not all values can be represented by a finite number of decimal digits (e.g., 95/100).

The value 0.94999999999999996 or 0.949999999999999955591079014994 is the closest representable value to 95/100.

solution:

var num = 22.415;
var roundedto = 2;
var n = Math.round(num *Math.pow(10,roundedto))/Math.pow(10,roundedto);