What pitfalls should be avoided when working on projects involving PHP, MySQL, and JavaScript?

One common pitfall to avoid when working on projects involving PHP, MySQL, and JavaScript is failing to properly sanitize user input before using it in SQL queries. This can lead to SQL injection attacks, where malicious code is injected into the query and executed on the database. To prevent this, always use prepared statements or parameterized queries to safely handle user input.

// Example of using prepared statements to sanitize user input in a MySQL query
$stmt = $pdo->prepare("SELECT * FROM users WHERE username = :username");
$stmt->bindParam(':username', $username);
$stmt->execute();