Question

I’ve got a web page that displays decimals in a user’s localized format, like so:

• English: 7.75
• Dutch: 7,75

If I add two number variables together in JavaScript on my machine (where the numbers are taken from strings in the above formats) I get the following results:

• English: 7.75 + 7.75 = 15.5
• Dutch: 7,75 + 7,75 = 0

If I was to run this code on a Dutch users machine, should I expect the English-formatted addition to return 0, and the Dutch-formatted addition to return 15,5?

In short: Does the JavaScript calculation use local decimal separators in its string to number conversions?

Answer 1

No, the separator is always a dot (.) in a javascript Number. So 7,75 evaluates to 75, because a , invokes left to right evaluation (try it in a console: x=1,x+=1,alert(x), or more to the point var x=(7,75); alert(x);). If you want to convert a Dutch (well, not only Dutch, let’s say Continental European) formatted value, it should be a String. You could write an extension to the String prototype, something like:

String.prototype.toFloat = function(){
      return parseFloat(this.replace(/,(\d+)$/,'.$1'));
};
//usage
'7,75'.toFloat()+'7,75'.toFloat(); //=> 15.5

Note, if the browser supports it you can use Number.toLocaleString

console.log((3.32).toLocaleString("nl-NL"));
console.log((3.32).toLocaleString("en-UK"));

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