JavaScript regex to limit number of characters and allow digits and no more than one letter

Question

I'm trying to make a regex that matches a string of digits and up to one letter (in any position), something like this:

^\d*[a-zA-Z]?\d*$

but the string must be between two and six characters long.

Eg these would be valid:

12  
a1  
12B3  
B12345  
123C45  
12345g 

but these would not be:

AB  
C123D 

Thanks in advance.

Answer 1

Your regex is fairly close, you just need to add a lookahead condition in your regex:

^(?=.{2,6}$)\d*[a-zA-Z]?\d*$

RegEx Demo

RegEx Details:

• ^ : Start
• (?=.{2,6}$) : Positive lookahead to assert that we have 2 to 6 characters ahead of start position
• \d* : Match 0 or more digits
• [a-zA-Z]? : Match an optional English letter
• \d* : Match 0 or more digits
• $ : End