How to Prevent fetch Objects from Executing Immediately in Node.js

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The Problem

You might find yourself in a situation where you want to create an array of fetch promise objects without triggering them right away. For instance, you could be working with a Netlify serverless function that requires you to run multiple processes in parallel. Attempting to create your array of promises can lead to confusion, especially when you see error messages that indicate an attempt to connect to a localhost address that isn’t set up to handle requests.

As per the example provided, trying to execute fetch on an object directly leads to immediate execution of the fetch call, resulting in errors. Here’s a snippet of the original code that illustrates this issue:

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Understanding Why Fetch Executes

The culprit behind the immediate execution of your fetch objects is the use of await within the createFetchObjectArray function. When you call fetchURL(obj) directly, it gets executed instantaneously, rather than setting it aside to be executed later.

The Solution: Deferring Execution

To prevent fetch from executing immediately, you'll want to change the way you build your array of promises. Instead of calling the function directly and pushing the result, you should push a function that calls fetchURL(obj) when invoked later.

Step-by-Step Implementation

Create a function that returns a fetch promise: Define your fetch call so that it returns a promise instead of executing it right away.

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

Populate the array with functions, not promises: Modify the createFetchObjectArray function to return an array of functions.

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

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

Complete Code Example

Here’s a cleaned-up version of your code that encompasses the solution effectively:

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

Conclusion

By adjusting the approach to building your promise array and using function wrappers to manage execution, you can easily defer fetch calls until you are ready to handle their responses. This not only prevents execution errors but also allows for efficient parallel processing of asynchronous requests.