call async function from non async

3 min read 22-10-2024

Calling Async Functions from Non-Async Functions: A Comprehensive Guide

In JavaScript, async/await functions make asynchronous code more readable and manageable. But what happens when you need to call an async function from a non-async function? This seemingly simple task requires a bit of understanding to ensure proper execution. Let's dive into the specifics and explore the best practices.

Understanding the Challenge

Async functions inherently return promises, a fundamental concept in JavaScript for handling asynchronous operations. While async functions gracefully handle promise resolution, non-async functions are not equipped to deal with them directly. This poses a challenge when attempting to call an async function within a non-async context.

The Solutions

There are two primary approaches to address this challenge:

Using .then():

The .then() method allows you to attach a callback function that will execute once the promise returned by the async function resolves. This is the traditional approach to handling promises.
```
async function fetchData() {
  return await fetch('https://api.example.com/data');
}

function processData() {
  fetchData()
    .then(response => response.json())
    .then(data => console.log(data))
    .catch(error => console.error(error));
}

processData(); // Call the non-async function
```
- Explanation: The fetchData() function is asynchronous and returns a promise. We chain .then() methods to handle the promise:
  - The first .then() converts the response to JSON format.
  - The second .then() logs the data to the console.
  - The .catch() handles any potential errors during the process.
Using async/await with a Promise.resolve():

This approach involves wrapping the async function call within Promise.resolve(), which creates a new promise that resolves immediately, allowing you to use async/await in your non-async function.
```
async function fetchData() {
  return await fetch('https://api.example.com/data');
}

function processData() {
  Promise.resolve()
    .then(async () => {
      const data = await fetchData();
      console.log(data);
    })
    .catch(error => console.error(error));
}

processData(); // Call the non-async function
```
- Explanation: The Promise.resolve() creates a promise that resolves immediately. The .then() method allows you to handle the resolution, where you use async/await to call fetchData() and handle its returned promise.

Choosing the Right Method

Both methods effectively handle async functions within non-async contexts. The choice depends on your preference and coding style.

.then() is more traditional and works well for simpler scenarios.
Promise.resolve() with async/await provides a more readable syntax for complex asynchronous operations.

Practical Example: Fetching Data from an API

Let's imagine a scenario where you're building a web application that needs to fetch data from an API. You can utilize an async function to handle the API request and a non-async function to process the received data.

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

// Non-async function to process the data
function processData() {
  fetchData()
    .then(data => {
      // Process the received data
      console.log(data);
      // Update the user interface, etc.
    })
    .catch(error => console.error(error));
}

// Call the non-async function to initiate the process
processData();

This example demonstrates how to handle asynchronous API calls within a non-async function. The code snippet demonstrates how to fetch data, process it, and handle potential errors gracefully.

Key Takeaways

Calling async functions from non-async functions is achievable by leveraging promises and the .then() method or by using Promise.resolve() with async/await.
Choose the approach that aligns with your project's complexity and your coding style.
Always handle potential errors gracefully by using .catch() or a similar error handling mechanism.

By mastering the techniques for calling async functions from non-async functions, you can confidently integrate asynchronous operations into your JavaScript applications, resulting in cleaner, more efficient, and more readable code.