Question

I am looking to create a regular expression in javascript that does the following:

1. Allows for 1 or more numbers
2. Then has an optional period (“.”)
3. Then has an optional number of digits up to 6

The context is that i need people to enter in numeric values in the millions and i want them to at least include a 0 if they are entering thousands… so they could enter the following:

1 (would be one million)
0.725 (would be 725k)
10.5 (would be 10M 500K)

I also need to ensure that the value doesn’t reach over 725.00 (or 725 million).

Thanks in advance.

Answer 1

So basically you want a number that would be multiplied by 10^6 to get the true value.

This sounds like a two-stepper; First, verify that the input string is in a format you expect (you can use a regex for this very easily). Then, parse the string into a number variable and test the actual value. The regex pattern for that would look like "[0-9]{1,3}(\.[0-9]{1,6})?", basically matching a number with up to 3 whole digits and 6 fractional digits, the decimal place and fractional digits being optional. If it matches this pattern, then it’s parsable into a number, and you can then perform a quick check that your number <= 725.

I honestly don’t think it’s feasible to create a single Regex that can validate a proper numeric format AND an inclusive maximum range, but here’s a start:

"^(725(\.0{1,6})|(([7][2][0-4]|[7][0-1][0-9]|[1-6][0-9]{2}|[1-9][0-9]|[0-9])(\.[0-9]{1,6})?)$"

This will allow any natural whole number from zero to 724, with any fractional part up to six digits from “.000001” to “.999999”. It does this in stages; it will match 720-724, or 700-719, or any three-digit number up to 699, or any two-digit number, or any one-digit number. Then, it will also match the quantity “725” explicitly, with an optional decimal point and up to 6 zeroes.

EDIT: While your comment states that you used this pattern, and it does produce the correct result, I had intended it as a “what not to do”; this pattern will be far more costly to evaluate than the first solution, just to avoid a server-side rule check. And you will have to perform a server-side validation anyway; anything done within the confines of the user’s browser should be suspect because the user can disable JavaScript or can even use browser plug-ins like FireBug to make your HTML page behave the way he wants, instead of the way you designed it.