Pattern works in Chrome, but not jsdom

[stnguyen90]

Basic info:

• Node.js version: v20.8.0
• jsdom version: 24.0.0

Minimal reproduction case

const jsdom = require('jsdom');
const { JSDOM } = jsdom;

const pattern = String.raw`^(?!-)[[A-Za-z0-9\-]]+([[\-\.]]{1}[[a-z0-9]]+)*\.[[A-Za-z]]{2,18}$`;
const value = 'not-a-domain';
const dom = new JSDOM(`<input id="domain" pattern="${pattern}" required value="${value}">`);

const input = dom.window.document.querySelector("#domain");

console.log('pattern:', input.pattern);
console.log('value:', input.value);
input.checkValidity();
console.log('validity.valid:', input.validity.valid); // returns true
console.log('validity.patternMismatch:', input.validity.patternMismatch); // returns false

How does similar code behave in browsers?

In the browser, input.validity.valid is false and input.validity.patternMismatch is true. You can test this by pasting this code:

<input id="domain" pattern="^(?!-)[[A-Za-z0-9\-]]+([[\-\.]]{1}[[a-z0-9]]+)*\.[[A-Za-z]]{2,18}$" required value="not-a-domain">

<input id="domain" pattern="^(?!-)[[A-Za-z0-9\-]]+([[\-\.]]{1}[[a-z0-9]]+)*\.[[A-Za-z]]{2,18}$" required value="example.com">

into MDN's pattern docs:

In jsdom's source code, I noticed the u flag being used for the RegExp:

https://github.com/kontomondo/jsdom/blob/c8f6f2504a71aa904f76b5bd4359505fc4820860/lib/jsdom/living/nodes/HTMLInputElement-impl.js#L806

According to MDN:

Would it be okay to update the source accordingly?