feat(isSlug): isSlug validator

[Nicanor008]

Closes #952

[profnandaa]

Really great for your first PR @Nicanor008! I'll review soon. Thanks 🎉

[ezkemboi]

I have requested some slight changes and gave comments and some appropriate solutions on the same.

[ezkemboi]

Good work on this. Here are my comments and some changes request:

1. Use of camel casing e.g

let regexCharset = new RegExp(`${charset}`)

2. We can make some changes instead of using new Regex example provided

let charsetRegex = /^([a-z0-9\\-]{1,})$/;
// remove let regex_charset = new RegExp(`${charset}`);
// Other code remains the same
return (
      charsetRegex.test(str) && 
      // Other code here
 )

3. Also, we can make the regex further combined

import assertString from './util/assertString';

let charsetRegex = /^[^-_](?!.*?[-_]{2,})([a-z0-9\\-]{1,}).*[^-_]$/;

export default function isSlug(str) {
  assertString(str);
  return (charsetRegex.test(str));
}

[Nicanor008]

thanks for this Feedback @ezrqnkemboi, makes good use of the re-usable variable.

[ezkemboi]

Add other invalid cases such as:

-not-slug,
not-slug-,
_not-slug,
not-slug_,

[ezkemboi]

Also, update the README file.

[Nicanor008]

thanks, @ezrqnkemboi I'll work on the feedback

[Nicanor008]

Feedback implemented @ezrqnkemboi
cc: @profnandaa

[ezkemboi]

Changes I requested were implemented here.

[profnandaa]

LGTM, thanks for your contrib! 🎉