Event Providers

Package yarn is required for this guide, run /pully install yarn to install the package.

You should also add yarn as a dependency in package.json.

FabricMC allows you to listen to events by defining a function which is ran whenever the event occurs.

In JSCore, you can define a runnable which will be ran whenever a specific event occurs. Each different type of event requires different types of runnable.

• jscore.Core (or just Core) provides runnables for registering commands.
• yarnwrap.Core provides runnables for all Fabric API events.

When creating runnables, you can specify which Core should the runnable use.

// `Core` aliases to `jscore.Core`
let jscoreRunnable = Core.runnable.create(
  "jscore-runnable",
  "function main() { console.log('hi') }",
);

let yarnwrapRunnable = yarnwrap.Core.runnable.create(
  "jscore-runnable",
  "function main() { console.log('hi') }",
);

Runnables created using requireRunnable() can use an additional argument to specify the Core.

// not specified: defaults to jscore.Core
let jscoreRunnable = requireRunnable("file.js");
let yarnwrapRunnable = requireRunnable("file.js", yarnwrap.Core);

Listening to Events

Suppose we want to run some code on every tick, in the Fabric API events index we can listen to ClientTickEvents.END_WORLD_TICK, which is called at the end of every world tick.

If we want to print out our coordinates at every tick, we can write a function that is ran every world tick.

// modules/my_module/onTick.js

// although END_WORLD_TICK gives ClientWorld as a parameter,
// We don't actually need it.
function onTick(_world) {
  let playerEntity = yarn.playerEntity;
  let x = Math.round(playerEntity.x);
  let y = Math.round(playerEntity.y);
  let z = Math.round(playerEntity.z);
  console.log(`x=${x}, y=${y}, z=${z}`);
}

yarn.playerEntity is provided by yarn.js, see Yarnwrap index for methods provided by each class.

Because we are listening to a Fabric API event, create a runnable with yarnwrap.Core.

// modules/my_module/entry.js
let onTickRunnable = requireRunnable(
  "modules/my_module/onTick.js",
  yarnwrap.Core,
);

ClientTickEvents.END_WORLD_TICK.register(onTickRunnable);

ClientTickEvents along with other event imports are provided by yarn.js.

However the listener is re-registered each time the script is reloaded, and it is not possible to remove a listener once added. Therefore it is recommended to use modtoggle to listen to events.