calling async function from non async

Charlotte

2 min read

·

01-03-2025

1

0

Share

Async functions are a powerful feature of JavaScript, allowing for cleaner asynchronous code. However, you might encounter situations where you need to call an async function from a non-async (synchronous) function. This article explains how to handle this, along with best practices and potential pitfalls. Understanding how to manage this effectively is crucial for writing robust and efficient JavaScript applications.

Understanding Async/Await

Before diving into the solutions, let's briefly recap async/await. Async functions always return a Promise. The await keyword can only be used inside an async function. It pauses execution until the Promise resolves (or rejects). This makes asynchronous code look and behave a bit more like synchronous code, improving readability.

Method 1: .then() and .catch()

The most straightforward method for calling an async function from a synchronous context is using the .then() method to handle the resolved Promise and .catch() to handle any rejected Promises.

async function myAsyncFunction() {
  // Simulate an asynchronous operation
  await new Promise(resolve => setTimeout(resolve, 1000)); 
  return "Async operation complete!";
}

function mySyncFunction() {
  myAsyncFunction()
    .then(result => {
      console.log("Result:", result); // Handle successful resolution
    })
    .catch(error => {
      console.error("Error:", error); // Handle rejection
    });
  console.log("Sync function continues execution immediately.");
}

mySyncFunction();

In this example, mySyncFunction calls myAsyncFunction. The .then() block executes once myAsyncFunction's Promise resolves. The console.log statement in mySyncFunction shows that the synchronous function continues execution without waiting for the asynchronous operation.

Method 2: async Wrapper Function

Another approach is to wrap the call to the async function within another async function:

async function myAsyncFunction() {
  // ... (same as before) ...
}

function mySyncFunction() {
  (async () => {
    try {
      const result = await myAsyncFunction();
      console.log("Result:", result);
    } catch (error) {
      console.error("Error:", error);
    }
  })();
  console.log("Sync function continues execution immediately.");
}

mySyncFunction();

This creates an immediately invoked asynchronous function expression (IIFE). This encapsulates the await keyword, allowing you to handle the Promise within the async IIFE without modifying mySyncFunction. Error handling is also included using a try...catch block.

Choosing the Right Method

Both methods achieve the same outcome: calling an async function from a synchronous one. The choice often depends on personal preference and code structure.

• .then().catch(): More concise if you only need simple success/failure handling.

• async Wrapper: Better suited for more complex error handling or when you need to perform additional operations after the async function completes within the same scope. It promotes cleaner error handling, especially if you have several await calls inside the wrapper.

Important Considerations

• Non-blocking nature: Remember that even with these methods, the synchronous function doesn't wait for the async function to complete. If you need the result of the async function before proceeding, you must use one of these methods and handle the Promise resolution.

• Error handling: Always include error handling (catch blocks or try...catch statements). Unhandled rejections can lead to unexpected behavior.

• Context: Be mindful of the this context. If your async function relies on this, make sure it's properly bound within the context you call it from.

By understanding these methods and their nuances, you can effectively manage asynchronous operations within your JavaScript applications, even when dealing with synchronous function calls. Remember to prioritize clear, maintainable, and robust code.