Understanding Async/Await in JavaScript

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3 years ago

Understanding Async/Await in JavaScript

In this post, we will give you information about Understanding Async/Await in JavaScript. Here we will give you detail about Understanding Async/Await in JavaScriptAnd how to use it also give you a demo for it if it is necessary.

Async/await lets you write async code in a way that looks like sync code. You can
use if statements, for loops, and try/catch in async functions!

Async

The async keyword marks a function as an async function. In the below example, test() is an
async function.

async function test() {
  return 42;
}

You can also define an async arrow function:

const test = async () => 42;

Await

The special thing about async functions is that you can use the await
keyword. If you await on a promise, the await keyword pauses execution of
the surrounding async function until the promise fulfills or rejects. await also unwraps the promise: it
gives you the fulfilled value of the promise.

async function test() {
  // 'await' unwraps the promise's value
  const val = await Promise.resolve(42);
  val; // 42
}

test();

In the above example, the Promise.resolve() function means the promise is fulfilled immediately. In the below example,
await pauses execution of test() for 100 ms:
‘

async function test() {
  const start = Date.now();
  await new Promise(resolve => setTimeout(resolve, 100));
  const elapsed = Date.now() - start;
  elapsed; // about 100
}

await is just a plain old JavaScript keyword. That means you can use it within
if statements, for loops, and try/catch.

async function asyncEvenNumbers() {
  const nums = [];
  for (let i = 1; i <= 10; ++i) {
    if (i % 2 === 0) {
      const v = await Promise.resolve(i);
      nums.push(v);
    }
  }

  nums; // [2, 4, 6, 8, 10]
}

Return Value

Another special property of async functions is that they always return a promise.
Even if you return a primitive value from an async function, JavaScript will
wrap that value in a promise.

async function test() {
  return 42;
}

const p = test();
p instanceof Promise; // true
p.then(v => {
  v; // 42
});

That means can use await on an async function call:

async function test() {
  return 42;
}

async function main() {
  const val = await test();
  val; // 42
}

Error Handling

Error handling with async/await is a complex topic. But, at a high level,
there are two patterns for handling errors.

When you await on a promise and that promise rejects, await throws an
error that you can try/catch:

async function test() {
  try {
    await Promise.reject(new Error('Oops'));
  } catch (err) {
    err.message; // Oops
  }
}

You can also use the Promise#catch() function to unwrap the promise’s error:

async function test() {
  const promise = Promise.reject(new Error('Oops'));

  // Unwrap the promise's error
  const err = await promise.catch(err => err);
  err.message; // 'Oops'
}

Async/await is the future of concurrency in JavaScript. “Mastering Async/Await”
teaches you how to build frontend and backend apps using
async/await in just a few hours.
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JavaScript Fundamentals for nderstanding Async/Await in JavaScript

JavaScript is a programming language that is used to create interactive web pages. It is a client-side scripting language, which means that it runs on the user’s browser. JavaScript can be used to add animation, interactivity, and functionality to web pages.

Here are some of the fundamentals of JavaScript:

Variables: Variables are used to store data. They are declared using the var keyword.
Data types: JavaScript has a variety of data types, including strings, numbers, booleans, objects, and arrays.
Operators: Operators are used to perform operations on data.
Control flow statements: Control flow statements allow you to control the order in which your code is executed.
Functions: Functions are blocks of code that can be reused.
Objects: Objects are used to store data in key-value pairs.
Arrays: Arrays are used to store data in a sequential order.
Events and event handlers: Events are notifications that are sent by the browser when something happens, such as when the user clicks on an element or moves the mouse over an element. Event handlers are functions that are called in response to an event.
DOM manipulation: The Document Object Model (DOM) is a tree-like structure that represents the elements of a web page. JavaScript can be used to manipulate the DOM to change the appearance or behavior of a web page.

These are just some of the fundamentals of JavaScript. There are many other concepts that you can learn as you continue to develop your skills.

Here are some resources that you can use to learn more about JavaScript:

Mozilla Developer Network (MDN): The MDN is a great resource for learning about JavaScript. It has a comprehensive reference guide, tutorials, and articles on a wide range of topics.
W3Schools: W3Schools is another great resource for learning about JavaScript. It has interactive tutorials and quizzes that can help you learn the basics of the language.
JavaScript.info: JavaScript.info is a website that provides in-depth tutorials on JavaScript. It also has a forum where you can ask questions and get help from other JavaScript developers.

I hope this helps!

Here are some additional tips for learning JavaScript:

Start with the basics: Before you start trying to build complex applications, it’s important to learn the basics of JavaScript. This includes things like variables, data types, operators, and control flow statements.
Practice regularly: The best way to learn JavaScript is to practice regularly. Try to find some time each day to work on JavaScript projects.
Get help from others: If you get stuck, don’t be afraid to ask for help from others. There are many online forums and communities where you can get help from other JavaScript developers.

With a little practice, you’ll be able to learn JavaScript and start building amazing web applications.

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