RegEx for at least 1 number, 1 lower case and 1 upper case letter

Question

Currently, I'm using one that I found with a length restriction:

<input #password="ngModel" type="password" name="password"  minlength="5" maxlength="30" pattern="((?=.*\d)(?=.*[a-z])(?=.*[A-Z]).{6,20})" required ngModel>

It works, but I don't want the length restriction at the end. I don't know much about regular expressions, so I assumed that removing {6,20} at the end would get the job done, but I was wrong.

So my question is: How do I make this regex work without the length restriction? Thanks!

Answer 1

You are using an HTML5 pattern attribute that anchors a regex by default (it actually wraps the pattern with ^(?: and )$). That means the pattern must match the entire string. This is the reason why you can't just take out .{6,20} and keep the lookaheads.

You need to use the lookaheads at the beginning, and .* (to allow 0 or more chars in the input) or .+ (to disallow empty input) at the end (as the consuming pattern part):

pattern="(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*"

This will be successfully translated into /^(?:(?=.*\d)(?=.*[a-z])(?=.*[A-Z]).*)$/ and will work as expected:

• ^ - start of string
• (?: - start of the non-capturing group
  • (?=.*\d) - 1 digit after any 0+ chars from the current position is required
  • (?=.*[a-z]) - 1 lowercase letter after any 0+ chars from the current position is required
  • (?=.*[A-Z]) - 1 uppercase letter after any 0+ chars from the current position is required
• .* - any 0 or more chars
• ) - end of the non-capturing group
• $ - end of string.