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Discover how to properly manage async functions in Node.js to avoid errors when creating and seeding a PostgreSQL database.
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How to Ensure Your Async Functions Run in Order in Node.js

When working with Node.js, especially in situations involving databases, correctly managing asynchronous operations is critical. A common issue developers encounter is having one async function execute before another one has completed, leading to errors such as “relation 'public.user' does not exist.” In this guide, we will explore this issue and how to ensure that your async functions run sequentially.

The Problem: Async Function Execution Order

In the scenario described, a developer is trying to create a user table and then seed it with users in PostgreSQL. However, the second async function seedUserTable is being called before createUserTable has finished executing. This premature execution of the second function leads to the following error:

[[See Video to Reveal this Text or Code Snippet]]

This error occurs because the second function tries to insert data into the public.user table that hasn’t been created yet!

Understanding the Code

Let's break down the initial code to see what’s happening under the hood:

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Sequential Execution of Async Functions

The key takeaway here is that when you call createUserTable() and seedUserTable() directly, they initiate independently and do not wait for each other. Because of this, even if createUserTable is still running, seedUserTable kicks off and tries to access the table that hasn't yet been created.

The Solution: Using Async/Await Properly

The solution to this problem is to designate a proper sequence for the async function calls using the async/await syntax:

Updated Code Implementation

Instead of calling both functions directly, wrap the calls in an async IIFE (Immediately Invoked Function Expression):

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Solution

Wrap in IIFE: This immediately invokes an async function, allowing you to use await within it.

Use await: By adding await, we ensure that the execution waits for createUserTable to complete before moving to seedUserTable.

This sequential execution is what allows us to avoid errors related to the database table not existing when the second function is called.

Conclusion

Managing async functions in Node.js can be tricky, especially when they interact with databases like PostgreSQL. By understanding the importance of execution order and utilizing async/await properly, developers can avoid common pitfalls that may arise.

Key Takeaways

Always ensure that async functions that depend on each other are called sequentially.

Use await to make the execution flow more manageable and readable.

Wrapping your async calls in an IIFE is a handy technique when you need to use await at the top level.

By following these practices, you can ensure smoother operation in your Node.js applications, particularly when working with databases.