How can I check if a string is starting with a dot '.' and also have ':' in any other position?

Hoped that ^[.][:]* should achieve that, but looks like not.

CodePudding user response：

You may use:

/^\..*:/s

Sample script:

console.log(/^\..*:/s.test('.abc:def')); // true
console.log(/^\..*:/s.test('abc:def'));  // false

CodePudding user response：

The ^[.][:]* pattern matches a dot at the start of the string and then zero or more colons.

You need to allow any chars other than a : between the . and ::

/^\.[^:]*:/

It will match

• ^ - start of string
• \. - a dot
• [^:]* - any zero or more chars other than a :
• : - a colon.

See the regex demo.

JavaScript demo:

const texts = ['.abc\ndef:',  '.abc'];
const re = /^\.[^:]*:/;
for (const text of texts) {
  console.log(text, '=>', re.test(text))
}

CodePudding user response：

You might also write the check without a regex usin startsWith and includes:

const check = s => s.startsWith(".") && s.includes(":");
[
  ".abc:def",
  "abc:def",
  ":.",
  "."
].forEach(s =>
  console.log(check(s))
);