Vehicle script cross-referencing

In MTR 4, a script entry are defined separately from a vehicle object. (vehicles vs vehicleScripts) in order to maximize flexibility. (e.g. Re-using scripts across cars)

One downside of this approach is that script developers may forget to reference the scriptId in the vehicle object. This results in the scripts being loaded, but there's no effect for the vehicle.

To alleviate this, JCM will refuse to load the script (And display a warning in the console) if there's no vehicle referencing the script in the same resource pack.

You can bypass this by adding "forceLoad": true to the script entry and allow JCM to load it anyway.

Use cases

Sharing script entries in MTR 3 format

Under the MTR 3 / NTE format, the script object is contained inside the train object. Therefore each train must load it's own script entry if it wants to use scripting. This may result in a waste of power needing to parse the same script twice. (Or if your script have some information you want to share between them)

One way to work around this is to leverage the MTR 4 format to define a single script entry, which can be referenced by MTR 3 trains.

This can be done by renaming your MTR 3's mtr_custom_resources.json to mtr_custom_resources_pending_migration.json (If you have not done that already).
After that define a shared script entry in mtr_custom_resources.json in MTR 4 format, with "forceLoad": true.

You can then add the script_id field in MTR 3's train object, replacing scriptLocation/scriptText, and now you can reference the same script_id across multiple trains.

This would be guarenteed to work under the same resource pack, since JCM always read mtr_custom_resources.json before reading mtr_custom_resources_pending_migration.json, so the MTR 4 script entry is always defined first, before being referenced by other MTR 3 trains.

Cross Resource Pack Script Referencing

While highly not recommended (And not as practical/required), this approach allows scripts to be used across resource packs.

By adding "forceLoad": true, this ensures the script entry would remain loaded, allowing other resource packs to reference the same script id.

Note: This is dependent on the order you put your resource pack in. The pack containing the script entries must be loaded first, before it gets referenced by other resource packs.