Understanding the Behavior of export and export default in JavaScript

Explore the differences between `export` and `export default` in JavaScript, and learn how to manage configuration loading to ensure it's only executed once in your NodeJS applications.
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Understanding the Behavior of export and export default in JavaScript

The Problem at Hand

The question is, when you import this module in multiple files, will the loading function run each time, or will it simply provide a reference to a single object? Additionally, you want to ensure that the configuration values remain unchanged during the execution of your application.

Understanding export and the Execution Context

Before diving into a solution, let's clarify how JavaScript handles module imports and exports:

Single Execution: In JavaScript, everything in the file scope executes only once. When a module is imported, the code in that module runs once, and the exports are available by reference in subsequent imports.

Function Invocation: Any function declared outside another function will be called exactly once when the file is imported, not every time it is referenced.

Example of Execution

Consider the following simple setup to illustrate this:

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

The Right Approach for Configuration Loading

Now, back to your configuration scenario. You want to ensure loadConfig() runs only once. Here’s how you can implement that correctly:

As Is

Initially, you might have something like this:

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

While this works, it isn’t very clear about when loadConfig() gets executed.

Refined Solution

Instead, store the results of loadConfig() in a variable and then export that variable:

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

This way, it's clear that loadConfig() is called just once during the module import, and its results are stored in the config variable to be used throughout your application.

Alternative for Multiple Executions

If you ever needed to call your loading logic multiple times (though you mentioned that you don't want this), you can export the function itself:

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

Conclusion

So, next time you set up configurations, remember to leverage the behavior of export and export default thoughtfully. Happy coding!