What is the decimal separator symbol in JavaScript?

Question

A thought struck me as I was writing a piece of JavaScript code that processed some floating point values. What is the decimal point symbol in JavaScript? Is it always

Answer 1

According to the specification, a DecimalLiteral is defined as:

DecimalLiteral ::
    DecimalIntegerLiteral . DecimalDigitsopt ExponentPartopt 
    . DecimalDigits ExponentPartopt 
    DecimalIntegerLiteral ExponentPartopt

and for satisfying the parseFloat argument:

1. Let inputString be ToString(string).
2. Let trimmedString be a substring of inputString consisting of the leftmost character that is not a StrWhiteSpaceChar and all characters to the right of that character.(In other words, remove leading white space.)
3. If neither trimmedString nor any prefix of trimmedString satisfies the syntax of a StrDecimalLiteral (see 9.3.1), return NaN.
4. Let numberString be the longest prefix of trimmedString, which might be trimmedString itself, that satisfies the syntax of a StrDecimalLiteral.
5. Return the Number value for the MV

So numberString becomes the longest prefix of trimmedString that satisfies the syntax of a StrDecimalLiteral, meaning the first parseable literal string number it finds in the input. Only the . can be used to specify a floating-point number. If you're accepting inputs from different locales, use a string replace:

function parseLocalNum(num) {
    return +(num.replace(",", "."));
}

The function uses the unary operator instead of parseFloat because it seems to me that you want to be strict about the input. parseFloat("1ABC") would be 1, whereas using the unary operator +"1ABC" returns NaN. This makes it MUCH easier to validate the input. Using parseFloat is just guessing that the input is in the correct format.

Answer 2

use:

theNumber.toLocaleString();

to get a properly formatted string with the right decimal and thousands separators

Answer 3

As far as I'm aware, javascript itself only knows about the . separator for decimals. At least one person whose judgement I trust on JS things concurs:

http://www.merlyn.demon.co.uk/js-maths.htm#DTS