KubeJS 1.20.1 Migration Reference

Source version Minecraft 1.20.1 / MBD2 1.0.xTarget version Minecraft 1.21.1 / MBD2 21.1.1

Legacy example	1.21.1 form	Status
onEvent('recipes', e => ...)	ServerEvents.recipes(e => ...)	KubeJS event migration
.inputItem(...)	.inputItems(...)	Current schema method
.inputFluid(...)	.inputFluids(...)	Uses SizedFluidIngredient
.setPerTick(true)	.perTick(true) or callback	Renamed
.setChance(0.2)	.chance(0.2) or callback	Renamed
.isFuel(true)	Configure Fuel Recipe Types in the Recipe Type editor	No current builder method
.inputGas/.inputSlurry/.inputPigment/.inputInfuse	.inputChemicals(...)	Unified Mekanism chemical
.inputGases/.inputInfusions/.inputSlurries/.inputPigments	.inputChemicals(...)	Plural forms from the old official Wiki are also removed
.inputMana/.inputEU/.inputEmber	No current KJS builder	Disabled in 21.1.1
.inputFluids('water 1000')	.inputFluids('1000x minecraft:water')	Current sized-ingredient format
.addData('key', '{...}')	addDataString or pass a real Tag	addData does not parse a JSON string
ui.getFirstWidgetById(...)	ui.selectId(...).findFirst().orElse(null)	New UIElement tree
widget.setOnPressCallback(...)	addEventListener / addServerEventListener	New UI event system

// 1.20.1 legacy — recognition only
onEvent('recipes', event => {
  event.recipes.mbd2.crusher()
    .inputItem('minecraft:iron_ingot')
    .setPerTick(true)
    .inputFE(20)
    .isFuel(true)
})

// 1.21.1 current
ServerEvents.recipes(event => {
  event.recipes.example.crusher()
    .id('example:crusher/iron')
    .inputItems('minecraft:iron_ingot')
    .perTick(r => r.inputFE(20))
})

Do not mechanically replace the namespace: the builder path comes from the actual Recipe Type ID. Fuel is configured as a set of fuel recipe types, not an .isFuel(true) flag on one recipe.

The old Wiki described slotName as a Trait name; that was incorrect. It must match a recipe slot name exposed by the Trait definition. uiName matches a Recipe Viewer UI content element name.