async/await is the way to handle asynchronous operations in JavaScript. Its core is to encapsulate Promise, making the code more intuitive. 1. The async function returns a Promise, and await is used to wait for the Promise to complete; 2. Use try/catch to catch errors, and you can manually throw exceptions according to the status code and handle them accordingly; 3. You can perform multiple tasks concurrently in conjunction with Promise.all to improve efficiency; 4. Be careful to avoid abuse of await and cause serial requests. You cannot directly use await in the top-level scope, and understand the error propagation mechanism.

Async/await is a very intuitive and concise way to handle asynchronous operations in modern JavaScript development. It is essentially a layer of encapsulation of Promise, making asynchronous code look more like synchronous code, making it easier to understand and maintain.

What is async/await?

Simply put, the async function is a function that returns a promise, and the await keyword can only be used inside the async function and is used to "wait" for a promise to complete. This can avoid the nesting and readability problems caused by traditional .then() and .catch() chain calls.

Let's give a simple example:

 async function fetchData() {
  const response = await fetch('https://api.example.com/data');
  const data = await response.json();
  return data;
}

In this example, we wait for the network request to be completed through await , instead of using .then() to process the result. This method is clear and more in line with people's reading habits.

How to correctly handle errors using try/catch?

Although async/await makes the code look more synchronous, the nature of asynchronous has not changed, so error handling is still important. The recommended approach is to wrap the await operation in try/catch block, so that exceptions can be caught in the event of an error.

 async function getUserData(userId) {
  try {
    const response = await fetch(`https://api.example.com/users/${userId}`);
    if (!response.ok) throw new Error('Request failed');
    return await response.json();
  } catch (error) {
    console.error('Failed to obtain user data:', error);
    // You can choose to throw an error or return the default value throw error;
  }
}

• Using try/catch is standard practice.
• An error can be thrown manually according to the response status code.
• After the error is captured, you can do logging, UI prompts, etc.

Use async/await with Promise.all

Promise.all is still a very useful tool when you need to execute multiple asynchronous tasks concurrently and wait for them to complete. Combined with async/await, the code can be both efficient and clear.

 async function getMultipleUsers(ids) {
  try {
    const promises = ids.map(id => fetch(`https://api.example.com/users/${id}`));
    const responses = await Promise.all(promises);
    const users = await Promise.all(res => res.json()));
    return users;
  } catch (error) {
    console.error('Batch fetching user failed:', error);
  }
}

The benefits of this writing are:

• All requests are carried out concurrently, with high efficiency;
• Process the response and parse JSON respectively through two await ;
• Any failure will trigger catch .

Notes and common misunderstandings

Although async/await is very convenient, there are some easy places to get stuck:

• Don't abuse await : If there is no dependency between multiple asynchronous operations, you should execute concurrently instead of serial waiting.

  ? Not recommended:

   const a = await getA();
  const b = await getB(); // In fact, it can be initiated at the same time as getA

  ? Recommended:

   const [a, b] = await Promise.all([getA(), getB()]);

• Await cannot be used directly in the top-level scope : await cannot be used directly in ordinary functions or global scopes, but can only be used in async functions.

• Note the error propagation mechanism : Exceptions not caught by try/catch will become unhandled Promise rejection, which may cause the program to crash.

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Basically that's it. async/await is not complicated, but to really use it well, you still have to understand the Promise mechanism behind it and how to reasonably organize the asynchronous process.

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