使用正则表达式匹配包含恰好 N 个字符的字符串

Question

I need to validate a string using JavaScript. The rules are at least one number, at least 1 letter, and a limit to 10 characters. All works fine for a string with less than 10 characters = return false but if I have more than 10 characters, it returns true witch is not right.

var secretS = '123456789aa';

and I try to validate with

/(?=[a-zA-Z0-9]*[a-zA-Z])[a-zA-Z0-9]{10}$/.test(secretS)

How to limit to 10 characters so string with more than 10 needs to return false?

UPDATE:

How to build regex validation for 9 alphanumerical characters, followed by a hyphen, followed by 5 alphanumerical characters. The valid string will be like WE17CLDEC-J6557

Answer 1

The rules are at least one number, at least 1 letter, and a limit to 10 characters.

Use

/^(?=\d*[A-Za-z])(?=[A-Za-z]*\d)[A-Za-z\d]{10}$/.test(secretS)

See proof .

EXPLANATION

--------------------------------------------------------------------------------
  ^                        the beginning of the string
--------------------------------------------------------------------------------
  (?=                      look ahead to see if there is:
--------------------------------------------------------------------------------
    \d*                      digits (0-9) (0 or more times (matching
                             the most amount possible))
--------------------------------------------------------------------------------
    [A-Za-z]                 any character of: 'A' to 'Z', 'a' to 'z'
--------------------------------------------------------------------------------
  )                        end of look-ahead
--------------------------------------------------------------------------------
  (?=                      look ahead to see if there is:
--------------------------------------------------------------------------------
    [A-Za-z]*                any character of: 'A' to 'Z', 'a' to 'z'
                             (0 or more times (matching the most
                             amount possible))
--------------------------------------------------------------------------------
    \d                       digits (0-9)
--------------------------------------------------------------------------------
  )                        end of look-ahead
--------------------------------------------------------------------------------
  [A-Za-z\d]{10}           any character of: 'A' to 'Z', 'a' to 'z',
                           digits (0-9) (10 times)
--------------------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string

9 alphanumerical characters, followed by a hyphen, followed by 5 alphanumerical characters

Use

/^[a-zA-Z\d]{9}-[a-zA-Z\d]{5}$/.test(secretS)

See proof .

EXPLANATION

--------------------------------------------------------------------------------
  ^                        the beginning of the string
--------------------------------------------------------------------------------
  [a-zA-Z\d]{9}            any character of: 'a' to 'z', 'A' to 'Z',
                           digits (0-9) (9 times)
--------------------------------------------------------------------------------
  -                        '-'
--------------------------------------------------------------------------------
  [a-zA-Z\d]{5}            any character of: 'a' to 'z', 'A' to 'Z',
                           digits (0-9) (5 times)
--------------------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string

Answer 2

 var secretS = '123456789aa'; console.log (/^(?=.*[a-zA-Z])(?=.*\d)[a-zA-Z\d]{10}$/.test(secretS));