It feels like I am missing something obvious here. This has been asked a number of times - and the answer usually boils down to:

var num = 4.5;
num % 1 === 0; // false - 4.5 is a decimal

But, this fails for

var num = 1.0; // or 2.0, 3.0, ...
num % 1 // 0

Unfortunately, these doesn't work either

num.toString() // 1
typeof num // "number"

I am writing a JavaScript color parsing library, and I want to process input differently if it is given as 1.0 or 1. In my case, 1.0 really means 100% and 1 means 1.

Otherwise, both rgb 1 1 1 and rgb 1 255 255 will be parsed as rgb 255 255 255 (since I am right now taking anything <= 1 to mean a ratio).

It feels like I am missing something obvious here. This has been asked a number of times - and the answer usually boils down to:

var num = 4.5;
num % 1 === 0; // false - 4.5 is a decimal

But, this fails for

var num = 1.0; // or 2.0, 3.0, ...
num % 1 // 0

Unfortunately, these doesn't work either

num.toString() // 1
typeof num // "number"

I am writing a JavaScript color parsing library, and I want to process input differently if it is given as 1.0 or 1. In my case, 1.0 really means 100% and 1 means 1.

Otherwise, both rgb 1 1 1 and rgb 1 255 255 will be parsed as rgb 255 255 255 (since I am right now taking anything <= 1 to mean a ratio).

• javascript

• So, if there's a decimal point, it's a percentage, otherwise it's just the integer value? – Jonathan M Commented Sep 14, 2011 at 19:46
• 1 I think you're out of luck since 1.0 === 1. – pimvdb Commented Sep 14, 2011 at 19:46
• 1 Short of getting it as a string, I don't think you have any options here. JavaScript does not make any real distinction between floats and integers. I'll be following the question though, I'm interested to see if there's a potential answer. – Alex Turpin Commented Sep 14, 2011 at 19:47
• Jonathan - yes, that is what I am hoping to do. – Brian Grinstead Commented Sep 15, 2011 at 14:08

6 Answers 6

Those numbers aren't actually decimals or integers. They're all floats. The only real difference between 1 and 1.0 is the notation that was used to create floats of equal values.

1 === 1.0; // true
parseInt('1') == parseInt('1.0'); // true
parseFloat('1') === parseFloat('1.0'); // true
parseInt('1') === parseFloat('1'); // true
// etc...

Also, to demonstrate that they are really the same underlying data type:

typeof(1); // 'number'
typeof(1.0); // 'number'

Also, note that 'number' isn't unambiguous in JavaScript like it would be in other languages, because numbers are always floats.

Let your script parse the input as string, then it will be a matter of checking if there is the point like this.

mystring.indexOf('.');

Check this example and this example.

Number.isInteger(4.5)

Number.isInteger() is part of the ES6 standard and not supported in IE11.

You'll have to do it when parsing the string. If there's a decimal point in the string, treat it as percentage, otherwise it's just the integer value.

So, e.g.:

rgb 1 1 1   // same as #010101
rgb 1.0 1 1 // same as #ff0101

Since the rgb is there, you're parsing the string anyway. Just look for . in there as you're doing it.

Well, as far as the compiler is concerned, there is no difference between 1.0 and 1, and because there is no difference, it is impossible to tell the difference between them. You should change it from 1.0 to 100 for the the percentage thing. That might fix it.

var num = 1;

and

var num = 1.0;

are the same. You mention that you want to treat them differently when given from a user. You will want to parse the difference when it is still a string and convert it to the appropriate number.