javascript - regex for alphanumeric and special character

Question

Trying to build regex for string (company/organisation name) with below conditions:

• no leading or trailing space
• no double space in between
• shouldn't allow only single character (alphanumeric or white listed)
• can start with alphanumeric or white listed character
• shouldn't allow any white listed character entered multiple times

regex for these: /(?! )([a-zA-Z0-9_\\.\\-#&])+([a-zA-Z0-9_\\.\\-#&\\s])*(?<! )$/

 console.log(/(?! )([a-zA-Z0-9_\\.\\-#&])+([a-zA-Z0-9_\\.\\-#&\\s])*(?<! )$/.test('_')); // shouldn't allow console.log(/(?! )([a-zA-Z0-9_\\.\\-#&])+([a-zA-Z0-9_\\.\\-#&\\s])*(?<! )$/.test('a')); // shouldn't allow console.log(/(?! )([a-zA-Z0-9_\\.\\-#&])+([a-zA-Z0-9_\\.\\-#&\\s])*(?<! )$/.test('abc abc')); // shouldn't allow console.log(/(?! )([a-zA-Z0-9_\\.\\-#&])+([a-zA-Z0-9_\\.\\-#&\\s])*(?<! )$/.test('_123')); // works fine console.log(/(?! )([a-zA-Z0-9_\\.\\-#&])+([a-zA-Z0-9_\\.\\-#&\\s])*(?<! )$/.test('# abc')); // works fine console.log(/(?! )([a-zA-Z0-9_\\.\\-#&])+([a-zA-Z0-9_\\.\\-#&\\s])*(?<! )$/.test('abc abc!')); // works fine console.log(/(?! )([a-zA-Z0-9_\\.\\-#&])+([a-zA-Z0-9_\\.\\-#&\\s])*(?<! )$/.test('abc abc# abc')); // works fine 

current regex doesn't match all the criteria and couldn't figure out what's the problem with regex ?

Answer 1

You may use

/^(?=.{2})(?!(?:[^_.#&!-]*[_.#&!-]){2})[a-zA-Z0-9_.#&!-]+(?:\s[a-zA-Z0-9_.#&!-]+)*$/

Details

• ^ - start of string
• (?=.{2}) - any 2 chars must be at the start
• (?!(?:[^_.#&!-]*[_.#&!-]){2}) - no 2 occurrences of _.#&!- chars in the string
• [a-zA-Z0-9_.#&-]+ - 1 or more allowed chars (other than whitespace)
• (?:\\s[a-zA-Z0-9_.#&!-]+)* - 0+ occurrences of
  • \\s - 1 whitespace
  • [a-zA-Z0-9_.#&!-]+ - 1+ letters, digits and some symbols
• $ - end of string.

JS demo

 var rx = /^(?=.{2})(?!(?:[^_.#&!-]*[_.#&!-]){2})[a-zA-Z0-9_.#&!-]+(?:\\s[a-zA-Z0-9_.#&!-]+)*$/; console.log(rx.test('_')); // shouldn't allow console.log(rx.test('a')); // shouldn't allow console.log(rx.test('abc abc')); // shouldn't allow console.log(rx.test('_123')); // works fine console.log(rx.test('# abc')); // works fine console.log(rx.test('abc abc!')); // works fine console.log(rx.test('abc abc# abc')); // works fine