index.html

<form action='index.php' method='post'>
<input name='title' type='text' placeholder='Title...' value=''>
<div class='articles-list'></div>
<br />
<textarea name='body' placeholder='Content...' ></textarea>
<br />
<a class='submit-button' href='#' />Submit</a>
<br />
<div class='error-message'></div>
</form>

main.js

'use strict';

// TODO A: Improve readability and documentation.
// TODO B: Implement an autocomplete functionality for the text input.
// TODO C: Preview file content when clicking on an autocomplete suggestion.
// TODO D: Display autocomplete suggestions only when the input is in focus.
// TODO E: Add error handling for the autocomplete suggestions in case of a network failure.

(() => {
	const submitButton = document.querySelector('.submit-button');
	const form = document.querySelector('form');
	const articleTitle = document.querySelector('input');
	const articleBody = document.querySelector('textarea');
	const autoCompleteList = document.querySelector('.articles-list');
	const errorMessage = document.querySelector('.error-message');
	const delay = 200;

	/**
	 * Create child element for the autocomplete list.
	 *
	 * @function createChildOption
	 * @param {string} articleName
	 * @returns {HTMLElement} The created child option element wrapped
	 */
	const createChildOption = (articleName) => {
		const childOption = document.createElement('div');
		childOption.textContent = articleName;
		childOption.addEventListener('click', () => {
			articleTitle.value = articleName;
			fetchArticleContent(articleName);
			clearAutoCompleteList();
		});
		return childOption;
	};

	/**
	 * Clear autocomplete list removing all child elements and hides the list
	 * from view.
	 *
	 * @function clearAutoCompleteList
	 */
	const clearAutoCompleteList = () => {
		autoCompleteList.innerHTML = '';
		autoCompleteList.style.display = 'none';
	}

	/**
	 * Handles errors that occur during data fetching.
	 *
	 * @function handleFetchError
	 * @param {Error} error - The error object thrown during the fetch operation
	 */
	const handleFetchError = (error) => {
 		console.error('Error fetching data:', error);
 		errorMessage.textContent = 'Unable load content. Please try again.';
 		errorMessage.style.display = 'block';
 	};

	/**
	 * Fetch an existing title of an article based on a search query
	 * and fill the autocomplete list.
	 *
	 * @function fetchArticleTitle
	 * @param {string} query
	 */
	const fetchArticleTitle = (query) => {
		fetch(`/api.php?search=${encodeURIComponent(query)}`)
			.then(response => {
				if (!response.ok) {
					throw new Error(`HTTP error: ${response.status}`);
				}
				return response.json();
			})
			.then(data => {
				autoCompleteList.innerHTML = '';
				if (data.content && data.content.length > 0) {
					data.content.forEach(articleName => {
						const childOption = createChildOption(articleName);
						autoCompleteList.appendChild(childOption);
					});
					autoCompleteList.style.display = 'block';
				} else {
					autoCompleteList.style.display = 'none';
				}
			})
			.catch(error => {
				clearAutoCompleteList();
				handleFetchError(error);
			});
	}

	/**
	 * Fetch the content of an article based on its title and fill textarea.
	 *
	 * @function fetchArticleContent
	 * @param {string} title
	 */
	const fetchArticleContent = (title) => {
    		fetch(`/api.php?title=${encodeURIComponent(title)}`)
			.then(response => {
				if (!response.ok) {
					throw new Error(`HTTP error: ${response.status}`);
				}
				return response.json();
			})
			.then(data => {
				articleBody.value = data.content;
				errorMessage.style.display = 'none';
			})
			.catch(error => {
				handleFetchError(error);
			});
	};

	/**
	 * Initializes the autocomplete functionality for the article title input.
	 *
	 * This function set up event listeners to provide autocomplete suggestions
	 * as the user types in the input field. Handle hiding the autocomplete list
	 * when the input loses focus.
	 *
	 * The autocomplete data are fetched after a delay to avoid too many
	 * requests in short time.
	 *
	 * @function autoComplete
	 */
	const autoComplete = () => {
		let autoCompleteTimeout = null;

		articleTitle.addEventListener('input', function () {
			const query = this.value.trim();

			clearTimeout(autoCompleteTimeout);
			clearAutoCompleteList();

			if (query.length === 0) return;

			autoCompleteTimeout = setTimeout(() => {
				fetchArticleTitle(query);
			}, delay);
		});

		/**
		 * Hide the autocomplete list with a delay when the input loses focus.
		 */
		articleTitle.addEventListener('blur', () => {
			setTimeout(() => {
				clearAutoCompleteList();
			}, delay);
		});
	}

	/**
	 * Validate the form fields before submitting the form.
	 *
	 * @function submitArticle
	 */
	const submitArticle = () => {
		submitButton.addEventListener('click', (e) => {
			if (articleTitle.value.trim() === '' || articleBody.value.trim() === '') {
				e.preventDefault();
				errorMessage.innerHTML = 'Fields shouldn\'t be empty.';
				errorMessage.style.display = 'block';
			} else {
				form.submit();
			}
		});
	};

	/**
	 * Calls submitArticle function on DOM loaded to set up the form submission.
	 * 
	 * @event DOMContentLoaded
	 */
	document.addEventListener('DOMContentLoaded', function() {
		autoComplete();
		submitArticle();
	});

})();