async/await

async and await are syntactic sugar over Promises that make asynchronous code look and behave like synchronous code.

1. async Function

Declaring a function async makes it return a Promise.

async function greet() {
  return "Hello";
}

greet().then(msg => console.log(msg)); // "Hello"

2. await

await pauses the function until the Promise resolves.

async function loadData() {
  let response = await fetch("https://api.example.com/data");
  let data = await response.json();
  console.log(data);
}

• Can only use await inside an async function
• It waits for the Promise to resolve

3. Try/Catch for Error Handling

Use try/catch to handle rejections.

async function getUser() {
  try {
    let res = await fetch("https://api.example.com/user");
    let user = await res.json();
    console.log(user);
  } catch (err) {
    console.error("Failed:", err);
  }
}

4. Parallel await with Promise.all

async function loadAll() {
  const [res1, res2] = await Promise.all([
    fetch("/api/one"),
    fetch("/api/two")
  ]);
  const data1 = await res1.json();
  const data2 = await res2.json();
}

5. Invalid Usage (Don't Do This)

await fetch("/url"); // ❌ SyntaxError: await is only valid in async functions

6. When to Use

Use async/await for:

• Cleaner, readable async logic
• Avoiding .then() chains
• Fetching API data
• Sequencing dependent async operations