the following is my regex

regex: /^[a-zA-Z] -.*(?=.*\d)(?=.*[a-zA-Z]).*-[0-9] -[a-zA-Z] -[0-9] $/

the overall rules is: alphabet-alphanumeric-number-alphabet-number

im having problem at .*(?=.*\d)(?=.*[a-zA-Z]).*

the expected output for it to get a successful result for the alphanumeric part is

1. abc123
2. 123abc
3. 1abc23
4. ab23ca

and fail if

1. abcde
2. 12345

but the result i get is all successful include the expected fail result

1. abc-abc-123-abc-123
2. abc-123-123-abc-123

i see that using lookahead will also get the input after the dash(-) of the alphanumeric that caused it to be successful although it is not the expected result

CodePudding user response：

You could try

^[a-zA-Z] -(?![a-zA-Z] -|\d -)[a-zA-Z0-9] -\d -[a-zA-Z] -\d $

It uses this negative lookahead to check the second subsequence is not only made by alphabets or numerics

(?![a-zA-Z] -|\d -) 

Alternatively, you can use this positive lookahead to check the second subsequence is made by a digit preceded any alphabets or the other way around

(?=[a-zA-Z] \d|\d [a-zA-Z]) 

It is important to use a lookahead to check it right at the start of the subsequence, and do not use .* in this situation since it might consume a - and checks the wrong sequence behind it.

You may check the test result here

CodePudding user response：

why not:

/([A-Za-z] [0-9] |[0-9] [A-Za-z] )/

-- or --

/[A-Za-z]/.test(val) && /[0-9]/.test(val)

var cases = [
    "abc123",
    "123abc",
    "1abc23",
    "ab23ca",
    // fail
    "abcde",
    "12345",
    "abc-abc-123-abc-123", // not clear if these should fail?
    "abc-123-123-abc-123"
];

cases.forEach(val => {
    var ok = /([A-Za-z] [0-9] |[0-9] [A-Za-z] )/.test(val)
    //var ok = /[A-Za-z]/.test(val) && /[0-9]/.test(val);
    console.log(val, ok);
});

CodePudding user response：

For the alphanumeric part, you can assert not only digits till the next hyphen.

Using a case insensitive match:

^[a-z] -(?!\d -)[a-z]*\d[a-z\d]*-\d -[a-z] -\d $

• ^ Start of string
• [a-z] - Match 1 chars a-z and -
• (?!\d -) Negative lookahead, assert not only digits followed by -
• [a-z]*\d[a-z\d]*- Match optional chars a-z, match a digit and optional chars a-z or a digit
• \d -[a-z] -\d Match digits - chars a-z - digits
• $ End of string

Regex demo

const regex = /^[a-z] -(?!\d -)[a-z]*\d[a-z\d]*-\d -[a-z] -\d $/i;
[
  "abc-abc-123-abc-123",
  "abc-123-123-abc-123",
  "abc-abcde-123-abc-123",
  "abc-12345-123-abc-123",
  "abc-ab23ca-123-abc-123",
  "abc-1abc23-123-abc-123"
].forEach(s =>
  console.log(`${s} --> ${regex.test(s)}`)
);