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async Keyword

Introduction

The async keyword is used to declare an asynchronous function in JavaScript. An asynchronous function always returns a Promise, even if it directly returns a simple value.

The async keyword was introduced as part of the Async/Await feature to make asynchronous code easier to read and write. Instead of chaining multiple .then() methods, developers can write asynchronous code that looks and behaves much like synchronous code.

In Node.js, the async keyword is commonly used with file operations, API requests, database queries, browser automation, and other asynchronous tasks.

For automation engineers, the async keyword is used extensively in frameworks such as Playwright, Puppeteer, WebdriverIO, and many Node.js libraries to simplify automation scripts.

In this tutorial, you’ll learn what the async keyword is, how it works, and how to use it effectively.

What is the async Keyword?

The async keyword is placed before a function declaration or function expression.

It tells JavaScript that the function is asynchronous and automatically returns a Promise.

Why Use the async Keyword?

The async keyword helps developers:

  • Write cleaner asynchronous code.

  • Improve code readability.

  • Reduce Promise chaining.

  • Simplify asynchronous workflows.

  • Improve maintainability.

  • Work seamlessly with await.

  • Handle asynchronous operations more naturally.

Syntax

async function functionName() {

    return value;

}

Example 1: Basic async Function

async function greet() {

    return "Hello World";

}

greet()

.then(function (message) {

    console.log(message);

});

Sample Output

Hello World

Example 2: Returning a Number

async function getNumber() {

    return 100;

}

getNumber()

.then(function (number) {

    console.log(number);

});

Sample Output

100

Example 3: Returning an Object

async function getUser() {

    return {

        name: "Rahul",

        city: "Delhi"

    };

}

getUser()

.then(function (user) {

    console.log(user);

});

Sample Output

{ name: 'Rahul', city: 'Delhi' }

Example 4: Using async with a Promise

async function loadData() {

    return Promise.resolve(

        "Data loaded."

    );

}

loadData()

.then(function (message) {

    console.log(message);

});

Sample Output

Data loaded.

Example 5: Arrow Function with async

const calculate = async () => {

    return 50 * 2;

};

calculate()

.then(function (result) {

    console.log(result);

});

Sample Output

100

Automation Testing Examples

The async keyword is widely used in automation frameworks to simplify asynchronous operations.

Playwright Example

Simulate opening an application.

async function openApplication() {

    return "Application opened.";

}

openApplication()

.then(function (message) {

    console.log(message);

});

Sample Output

Application opened.

Selenium Example

Launch a browser.

async function launchBrowser() {

    return "Browser launched.";

}

launchBrowser()

.then(function (message) {

    console.log(message);

});

Sample Output

Browser launched.

Cypress Example

Visit a webpage.

async function visitPage() {

    return "Page visited.";

}

visitPage()

.then(function (message) {

    console.log(message);

});

Sample Output

Page visited.

API Testing Example

Retrieve an API response.

async function fetchApi() {

    return "API response received.";

}

fetchApi()

.then(function (message) {

    console.log(message);

});

Sample Output

API response received.

Data-Driven Testing Example

Load test data.

async function loadTestData() {

    return "CSV file loaded.";

}

loadTestData()

.then(function (message) {

    console.log(message);

});

Sample Output

CSV file loaded.

Common Uses of the async Keyword

The async keyword is commonly used for:

  • Reading files.

  • Writing files.

  • API requests.

  • Database queries.

  • Browser automation.

  • User authentication.

  • Processing JSON data.

  • Uploading files.

  • Data validation.

  • Workflow automation.

Common Mistakes

Forgetting That async Returns a Promise

Even if an async function returns a simple value, it is automatically wrapped in a Promise.

Using await Outside an async Function

The await keyword can only be used inside an async function (unless using top-level await in supported ES modules).

Mixing Callbacks with async

Prefer using async and await together instead of mixing callbacks and Promise chains.

Best Practices

  • Use async for asynchronous functions.

  • Combine async with await for better readability.

  • Handle errors using try...catch.

  • Use meaningful function names.

  • Keep asynchronous functions focused on a single responsibility.

  • Avoid unnecessary Promise wrapping inside async functions.

  • Write clean and readable asynchronous code.

Conclusion

The async keyword simplifies asynchronous programming by automatically returning a Promise and allowing developers to write cleaner, more readable code. It forms the foundation of the Async/Await syntax, making asynchronous workflows much easier to understand compared to traditional Promise chaining.

For automation engineers, the async keyword is an essential part of modern JavaScript development. It is used extensively in browser automation, API testing, file handling, and database interactions. Mastering the async keyword is the first step toward effectively using await and writing professional Node.js automation scripts.

Frequently Asked Questions (FAQs)

What does the async keyword do?

It declares an asynchronous function that always returns a Promise.

Does an async function always return a Promise?

Yes. Even if you return a simple value, JavaScript automatically wraps it in a Promise.

Can I use await without async?

No. The await keyword can only be used inside an async function (except for supported top-level await in ES modules).

Why is the async keyword important?

It makes asynchronous code easier to read, write, and maintain.

Why is async widely used in automation testing?

Modern automation frameworks use asynchronous operations for browser interactions, API requests, file handling, and database operations. The async keyword simplifies these workflows.

Key Takeaways

  • The async keyword creates an asynchronous function.

  • Every async function automatically returns a Promise.

  • Returned values are wrapped in resolved Promises.

  • async works seamlessly with the await keyword.

  • It improves the readability of asynchronous code.

  • It reduces the need for long Promise chains.

  • Modern Node.js applications heavily rely on async.

  • Automation frameworks extensively use async.

  • Use try...catch for error handling in async functions.

  • Understanding the async keyword is essential before learning the await keyword.