JavaScript

Why JavaScript matters

JavaScript started as a browser language and became the common API of both frontend and backend when Node.js matured. The modern ecosystem encourages shared contracts across UI and server code.

• Single language across the stack reduces team friction.
• TypeScript adds compile-time safety for large apps.
• Async and callback models scale for IO-heavy tasks.

Core mindset

1. Prefer immutable patterns in UI components.
2. Split concerns: presentation, state, API, utility.
3. Always narrow and validate input from external systems.
4. Control side effects with explicit state handlers.

Mini async example

async function retryFetch(url, retries = 3) {
  for (let attempt = 0; attempt <= retries; attempt++) {
    try {
      const res = await fetch(url);
      if (!res.ok) throw new Error("temporary");
      return await res.json();
    } catch (error) {
      if (attempt === retries) throw error;
      const delay = 250 * Math.pow(2, attempt);
      await new Promise(r => setTimeout(r, delay));
    }
  }
}

Common errors to watch

• Forgetting to cancel duplicated requests.
• Over-fetching and rendering all responses at once.
• Not handling rejected promises consistently.
• Mutable state updates with stale closures.

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