JavaScript Async & DOM

When to use this skill

• Manipulating usage of fetch or XMLHttpRequest.
• Adding event listeners to DOM elements.
• Interacting with browser APIs (Local Storage, Navigator).

1. Async Data Fetching

• Fetch API: Use fetch() with async/await. Always check res.ok before parsing JSON.

  const res = await fetch('/api/data');
  if (!res.ok) throw new Error('Failed');
  const data = await res.json();
  

• AbortController: Use AbortController to cancel pending requests when components unmount or fast interactions occur.

2. event Delegation

• Listener Attachment: Attach listeners to a parent container rather than individual items for lists.

  list.addEventListener('click', (e) => {
    if (e.target.matches('.item-btn')) { ... }
  });
  

• Cleanup: Always use removeEventListener if listeners are attached to transient elements (or use { once: true } where applicable).

3. DOM Manipulation

• Performance: Minimize reflows. Read layout properties (offsetWidth, etc.) in a batch, then write styles in a batch.
• Fragments: Use DocumentFragment when appending multiple elements to the DOM at once.