Inject script or css into the dom

inject.js

/**
* @param {string[]} filePaths - Array of file paths to append to the document
* @returns {Promise<void>} - Promise that resolves when all files have been appended
* @usage appendScriptFilesToDocument(['script.js', 'style.css'])
*/
const appendScriptFilesToDocument = (filePaths) => {
	return new Promise((resolve, reject) => {
		let count = 0;
		const total = filePaths.length;

		if (total === 0) {
			resolve();
		}

		function appendFile(filePath) {
			let file;

			if (filePath.endsWith('.js')) {
				file = document.createElement('script');
				file.src = filePath;
			} else if (filePath.endsWith('.css')) {
				file = document.createElement('link');
				file.rel = 'stylesheet';
				file.href = filePath;
			} else {
				reject(new Error('Unsupported file type'));
			}

			if (!file) return reject(new Error('File could not be loaded'));

			file.addEventListener('load', () => {
				count++;
				if (count === total) {
					resolve();
				} else {
					appendFile(filePaths[count]);
				}
			});

			file.addEventListener('error', (err) => {
				reject(err);
			});

			document.head.appendChild(file);
		}

		appendFile(filePaths[0]);
	});
}