Question

I am trying to extract a number from a string. The number might be zero. Numbers appear like this: ‘+123’, ‘-8’ or ‘0’.

alert( '+123'.match(/[-?|+?]\d+/) );
alerts +123

alert( '-8'.match(/[-?|+?]\d+/) );
alerts -8

alert( '0'.match(/[-?|+?]\d+/) );
alerts null // why oh why?

How do I get ‘0’.match(/[-?|+?]\d+/) to return 0 instead of null?

Answer 1

The pattern

[-?|+?]

will match exactly one -, +, | or a ?. What you want is

[-+]?

which will match a - or a + one or zero times.

This will allow numbers like ‘123’ to pass as well. If you require the + sign, use this:

/0|[-+][1-9]\d*/