Getting numbers after decimal in Javascript

Question

I have a color picker, and the hue values returned are numbers between zero and 1. To create variations on the hue, I add .2 for 20%, .8 for 80% etc.

How can I keep the numbers going around the circle, so that when the number goes above 1, it subtracts the 1. How can I make this number into this number: 1.73540012511 ---> .7354

I tried using a "cents" javascript, (http://www.irt.org/script/6.htm) but this returned values greater than 1: http://jsfiddle.net/Se9Dn/

I can't use Math.min, because I want 1.2 to become .2 (not to have the colors all become red when they hit 1).

Thanks. :)

Edit: Confirming solution, with rounding added. Assuming you have an HSL color (Hue, Saturation, Luminosity) returned from Farbtastic and want to adjust Hue mathematically:

hslcolor  = (.73802938, .59832908, .948987);
colorStep = .2;
newcolor[0] = Math.round ( ((1*colorStep +hslcolor[0])%1)*10000 ) /10000;

Watch out those parenthesis are very tricky in there.

If it's greater than 1 just subtract 1 ...

Pointy
– Pointy

2012-08-10 11:59:35 +00:00
Commented Aug 10, 2012 at 11:59 — Pointy
– Pointy, Commented Aug 10, 2012 at 11:59

Sirko · Accepted Answer · 2012-08-10 12:10:36Z

5

You can use the modulo operator % (MDN docu).

So for adding, e.g., 0.8:

result = (result + 0.8) % 1;

EDIT

The modulo operator of JavaScript is actually more of a remainder operator.

Citing the ECMAScript spec Section 5.2:

The notation “x modulo y” (y must be finite and nonzero) computes a value k of the same sign as y (or zero) such that abs(k) < abs(y) and x−k = q × y for some integer q.

edited Aug 10, 2012 at 12:10

answered Aug 10, 2012 at 12:00

Sirko

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4 Comments

Pointy Over a year ago

No. That will always return an integer remainder, which is not at all what's requested here.

Pointy Over a year ago

Whoa, you're right ... I don't understand how that makes sense, but as I noted a moment ago I haven't had a drop of coffee this morning so parts of my brain aren't working.

CM Kanode Over a year ago

The code example in the answer will return NaN, since no value was set when the variable is declared above and used on the same line.

Pointy Over a year ago

@Sirko yes I guess my concept of % got stuck shortly after I learned C 30 years ago :-)

Pointy · Accepted Answer · 2012-08-10 12:06:54Z

1

You just subtract the integer:

function cent(amount) { return (+amount) - Math.floor(+amount); }

If the number can be negative, then the it depends on the semantics you want. I'll leave that as an exercise :-)

edited Aug 10, 2012 at 12:06

answered Aug 10, 2012 at 12:01

Pointy

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