I have the following Regular Expression which matches an email address format:
^[\w\.\-]+@([\w\-]+\.)+[a-zA-Z]+$
This is used for validation with a form using JavaScript. However, this is an optional field. Therefore how can I change this regex to match an email address format, or an empty string?
From my limited regex knowledge, I think \b matches an empty string, and | means "Or", so I tried to do the following, but it didn't work:
^[\w\.\-]+@([\w\-]+\.)+[a-zA-Z]+$|\b
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To match pattern or an empty string, use
^$|pattern
^ and $ are the beginning and end of the string anchors respectively.| is used to denote alternates, e.g. this|that.\b\b in most flavor is a "word boundary" anchor. It is a zero-width match, i.e. an empty string, but it only matches those strings at very specific places, namely at the boundaries of a word.
That is, \b is located:
\w and \W (either order):
^ and \w
\w\w and $
\wThis is not trivial depending on specification.
\b matches a word boundary. I think you can use ^$ for empty string.
I'm not sure why you'd want to validate an optional email address, but I'd suggest you use
^$|^[^@\s]+@[^@\s]+$
meaning
^$ empty string
| or
^ beginning of string
[^@\s]+ any character but @ or whitespace
@
[^@\s]+
$ end of string
You won't stop fake emails anyway, and this way you won't stop valid addresses.
An alternative would be to place your regexp in non-capturing parentheses. Then make that expression optional using the ? qualifier, which will look for 0 (i.e. empty string) or 1 instances of the non-captured group.
For example:
/(?: some regexp )?/
In your case the regular expression would look something like this:
/^(?:[\w\.\-]+@([\w\-]+\.)+[a-zA-Z]+)?$/
No | "or" operator necessary!
Here is the Mozilla documentation for JavaScript Regular Expression syntax.
Source: Stackoverflow.com