This pattern should be used for loading any local project file by any means, such as setting the
src of a new Image to load an image file; creating a Web Worker from a script file; using
XMLHttpRequest instead of
fetch; and so on. First use
getProjectFileUrl() to look up the real URL to retrieve, and then proceed to load it normally like you would have otherwise, but with the adjusted URL.
Some more details
Once you export your project to the web, you can once again fetch project files like "myfile.txt" directly, since the project is now uploaded to a web server and that URL will work as expected. So once exported,
getProjectFileUrl() just returns the same URL you gave it since nothing needs to be changed.
In mobile apps where the fetch might not normally work, Construct automatically detects if the given URL will work, and returns that if so, else substitutes it for a different URL that can be loaded instead. This ensures it works even in non-web exports where fetches might not normally work.
What URL does Construct use instead? When it has to substitute the URL, it will use a blob URL instead. This is a randomly generated URL that begins with
blob:, e.g. blob:https://preview.construct.net/3c1ca690-91cc-4120-bf6a-ddc02d8a22a3. This is basically a URL that refers to a local file, which means it can be fetched as if it was on the Internet, but it actually just loads something on the same device. Internally Construct represents local files with Blobs, and these URLs are generated by URL.createObjectURL(). In some cases you may see these types of URLs being shown in developer tools or while debugging, and it just means it's loading a local resource instead of getting something over the Internet.