CODEWITHSUNDEEP
javascript
Firehawk
Firehawk

Reputation: 23

Validate text with javascript RegEX

I'm trying to validate text with javascript but can find out why it's not working.

I have been using : https://regex101.com/ for testing where it works but in my script it fails

    var check = "test"
    var pattern = new RegExp('^(?!\.)[a-zA-Z0-9._-]+$(?<!\.)','gmi');
    if (!pattern.test(check)) validate_check = false;else validate_check = true;

What i'm looking for is first and last char not a dot, and string may contain [a-zA-Z0-9._-]

But the above check always fails even on the word : test

Upvotes: 2

Views: 1806

Answers (3)

The fourth bird
The fourth bird

Reputation: 163217

A few notes about the pattern:

  • You are using the RegExp constructor, where you have to double escape the backslash. In this case with a single backslash, the pattern is ^(?!.)[a-zA-Z0-9._-]+$(?<!.) and the first negative lookahead will make the pattern fail if there is a character other than a newline to the right, that is why it does not match test
  • If you use the /i flag for a case insensitive match, you can shorten [A-Za-z] to just one of the ranges like [a-z] or use \w to match a word character like in your character class
  • This part (?<!\.) using a negative lookbehind is not invalid in your pattern, but is is not always supported

For your requirements, you don't have to use lookarounds. If you also want to allow a single char, you can use:

^[\w-]+(?:[\w.-]*[\w-])?$
  • ^ Start of string
  • [\w-]+ Match 1+ occurrences of a word character or -
  • (?: Non capture group
    • [\w.-]*[\w-] Match optional word chars, a dot or hyphen
  • )? Close non capture group and make it optional
  • $ End of string

Regex demo

const regex = /^[\w-]+(?:[\w.-]*[\w-])?$/;
["test", "abc....abc", "a", ".test", "test."]
.forEach((s) =>
  console.log(`${s} --> ${regex.test(s)}`)
);

Upvotes: 0

Reflective
Reflective

Reputation: 3917

What about more simpler RegEx?

var checks = ["test", "1-t.e_s.t0", ".test", "test.", ".test."];
checks.forEach(check => {
  var pattern = new RegExp('^[^.][a-zA-Z0-9\._-]+[^.]$','gmi');
  console.log(check, pattern.test(check))
});

Your code should look like this:

var check = "test";
var pattern = new RegExp('^[^.][a-zA-Z0-9\._-]+[^.]$','gmi');
var validate_check = pattern.test(check);
console.log(validate_check);

Upvotes: 0

Ephellon Grey
Ephellon Grey

Reputation: 420

+$(?<!\.) is invalid in your RegEx

  1. $ will match the end of the text or line (with the m flag)
  2. Negative lookbehind → (?<!Y)X will match X, but only if Y is not before it

Upvotes: 1

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