UI Behavior Example

Current MBD2 Minecraft 1.21.1 / MBD2 21.1.1Current UI LDLib2 2.2.39

Create the element and ID in the editor, then attach server behavior with `onUI`.

// kubejs/server_scripts/mbd2_ui.js
MBDMachineEvents.onUI('example:processor', wrapper => {
  const { machine, ui } = wrapper.event
  const reset = ui.selectId('reset_button').findFirst().orElse(null)
  if (reset === null) return

  reset.addServerEventListener(UIEvents.MOUSE_DOWN, event => {
    if (event.button !== 0) return
    const data = machine.customData.copy()
    data.remove('uses')
    machine.setCustomData(data)
  })
})

This requires a UIElement with ID reset_button in the editor. Layout, LSS, components, propagation, and data binding are maintained by LDLib2; continue with LDLib2 KubeJS UI support and the UIElement API.

Modify the client Recipe Viewer UI

// kubejs/client_scripts/mbd2_recipe_ui.js
MBDRecipeTypeEvents.onRecipeUI('example:processor', wrapper => {
  const { recipe, ui } = wrapper.event
  const output = ui.selectId('main_output').findFirst().orElse(null)
  if (output === null) return

  output.addEventListener(UIEvents.HOVER_TOOLTIPS, event => {
    event.hoverTooltips = HoverTooltips.empty().append(`Recipe: ${recipe.id}`)
  })
})

onRecipeUI is a client recipe-type event, so it registers ordinary client UIElement listeners with addEventListener. Never mutate a machine or server storage here.

HoverTooltips.empty().append(...) takes Components; a JS string is coerced for you.

Which listener to use

Call	Runs on	Use for
addEventListener(type, cb)	Client	Tooltips, visual state, anything local
addServerEventListener(type, cb)	Server, via RPC	Machine and storage changes

A JavaScript lambda created inside the server onUI callback does not become client code — pick the listener explicitly.

Legacy; do not copy to 1.21.1 Minecraft 1.20.1 / MBD2 1.0.x

// ❌ Legacy Widget API — these methods do not exist on the 1.21.1 UI
ui.getFirstWidgetById('reset_button').setOnPressCallback(...)