<div class="projects-categories">
<button class="btn-projects-categories" id="all">All</button>
<button class="btn-projects-categories" id="web-design">Web Design</button>
<button class="btn-projects-categories" id="mobile-app">Mobile App</button>
<button class="btn-projects-categories" id="illustration">Illustration</button>
<button class="btn-projects-categories" id="photograph">Photography</button>
</div>
<script>
document.querySelector('.projects-categories').addEventListener('click', ({target})=>{
alert(target.id);
})
</script>
Пример использования делегирования событий