The Correct Way to Pass JavaScript Variables in Express Controllers

Learn how to effectively pass JavaScript variables in Express controllers, avoiding common mistakes and understanding parameter passing with helpful examples.
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The Correct Way to Pass JavaScript Variables in Express Controllers

Understanding how JavaScript handles variable passing can be a source of confusion, especially when integrating it into frameworks like Express. If you’ve encountered issues with variable passing in an Express controller, you’re not alone. In this guide, we will explore a common issue related to passing variables and how to resolve it with practical examples.

The Problem: Variable Passing in Express

Let's consider the following snippet from your Express controller:

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The Output

You receive output similar to this:

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The Cause of the Issue

Why Does This Happen?

In the function declaration:

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

You're expecting three distinct parameters. However, when you call the function like this:

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

You are passing a single object, which ends up mapping to only the first parameter (session). The other parameters become undefined because they are not unpacked from the object.

Solutions to the Problem

To easily resolve this issue, there are a couple of approaches you can take.

Solution 1: Pass Variables Individually

Instead of passing an object, you can adjust your invocation to send each variable separately:

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

This method aligns perfectly with the function definition which accepts three distinct arguments.

Solution 2: Update the Function Declaration

Alternatively, you can modify your function to accept a single object and destructure it within the function itself:

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

You can still make the call as before, passing the object in a structured form:

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

Note on Async/Await and .then

Finally, as a best practice, you don't need to use .then() after calling .save() since you’re already using the async/await pattern. You can return the value directly using:

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

Conclusion

By understanding how JavaScript handles variable passing, you can avoid common pitfalls and ensure your Express controllers function as expected. Whether you choose to pass variables individually or as an object, clarity in your function definitions will help in making your code more manageable and error-free.

By following these practices, you’ll not only improve your own coding skills but also contribute to writing cleaner, more effective code. Happy coding!