Regex for a string which do not start with a number and allow only alphanumeric

Question

I am trying to create a javascript regex for below conditions

• Allow Alphanumeric only
• But also allow underscore(_)
• Don't allow to start with a number
• Don't allow to start with an underscore

I have created a regex ^(?![0-9]|[_].*$).* which will work for last two conditions above. Please suggest how can I add an and condition to make it work for all above scenarios.

Answer 1

You may use the following regex:

^[A-Za-z]\w*$

Details

• ^ - start of string
• [A-Za-z] - any ASCII letter
• \w* - zero or more letters/digits/_
• $ - end of string.

To allow an empty string match, wrap the whole pattern with an optional non-capturing group:

^(?:[A-Za-z]\w*)?$
 ^^^           ^^