Regex to use as validation for disabling more than 2 letters in a row-CodePudding

I need a regex that checks if there are more than two letters.

It should only allow one letter.

But allow numbers.

For example

1a is good
1ab is bad
11 is good
11ab is bad

I have one, it also takes as wrong when there are any numbers... I do want to allow numbers. Just not more than one letter.

This is my rgex:

export const onlyOneCharacter = (string) => {
  return /^[A-Za-z]{0,1}$/.test(string) ? undefined : "wrong";
};

Returning undefined mean its correct, so it doesnt show any validation error.

CodePudding user response：

If there can be no two consecutive letters in the string, you can use

const texts = ["1a", "1ab", "11", "11ab"];
const onlyOneCharacter = (string) => {
  return /[A-Za-z]{2}/.test(string) ? "wrong" : "correct";
};
console.log( texts.map(onlyOneCharacter) )

If you need to check for two letters that are not necessarily consecutive, you can use

const texts = ["1a", "1ab", "11", "11ab"];
const onlyOneCharacter = (string) => {
  return /[A-Za-z][^A-Za-z]*[A-Za-z]/.test(string) ? "wrong" : "correct";
};
console.log( texts.map(onlyOneCharacter) )

Note that [A-Za-z][^A-Za-z]*[A-Za-z] regex searches for a letter, then zero or more non-letter chars, and then a letter anywhere inside the string.

If the pattern is matched, the result is wrong, else, the return value is correct.

CodePudding user response：

I would use

^\d*[a-z]?\d*$

See the regex demo

JavaScript Example

const onlyOneCharacter = (string) => {
  return /^\d*[a-z]?\d*$/.test(string) ? undefined : "wrong";
};

console.log(onlyOneCharacter("1a"));
console.log(onlyOneCharacter("1ab"));
console.log(onlyOneCharacter("11"));
console.log(onlyOneCharacter("11ab"));