Filter out numbers out of a text using regular expressions in javascript

Question

What will be the best way using javascript regular expression to get numbers out of text.. e.g.... I have "$4,320 text/followme" and I want to get 4320 out of this. However I want to avoid numbers after first occourance of an alphabet or any non alphabet other than a comma ','

so that if i have $4,320 t234ext/followme it will still return me 4320. The input will always have $ sign at the beginning

so the regular expression should return

 $4,320 text/followme          returns  4320
 $4,320 t3444ext/followme      return   4320
 $4,320 /followme              return   4320
 $4320 text/followme           return   4320
 $4320 t3444ext/followme       return   4320
 $4320 /follow4me              return   4320

Answer 1

string.split(/ /)[0].replace(/[^\d]/g, '')

Answer 2

The simplest regular expression you're possibly looking for is \D (any character that's not a numeral. There's a few of these "negated" expressions -- \d matches a numeral, \D matches non-numerals. \w matches "word" characters (alphanumeric plus the underscore), \W matches non-numeric. \s matches whitespace, \S matches non-whitespace characters).

So:

str = '$4,320 text/folowme';
number = str.replace(/\D/g,'');

should yield '4320' inside of number. The 'g' is important. It says do a global search/replace for all instances of that regex. Without it, you'll just lose the dollar sign. :)

Note that if you've got negative numbers or rationals (which can have two non-numeric characters in their representation, '-' and '.'), your problem gets a little bit harder. You could do something like:

number = str.replace(/[^-.0-9]/g,'');

Which will work as long your numbers are well formed -- as nobody does anything crazy like '4-5.0-9aaaa4z.2'.

To be safe, you could run that list bit through parseInt or parseFloat:

number = parseFloat(str.replace(/[^-.0-9]/g,''));

UPDATE

I spaced the requirement to avoid including subsequent numbers. If whitespace reliably delimits the end of the number you want, as it does in the examples, you could add a space or \s to the negated character class on that last example I gave, so it'd be something like this:

number = parseFloat(str.replace(/[^-.0-9\s]/g,''));

and it'll strip out the extra numbers just fine.

UPDATE 2

After thinking about this for a bit, using parseFloat means that you don't have to strip out everything -- just all the non-numeric characters before the number you want, and commas. So we can break this into two simpler regexes (and probably faster, especially since one of them is non-global). And then parseFloat will discard trailing non-numeric input for you.

number = parseFloat(str.replace(/,/g,'').replace(/^[^-0-9]*/,''));