MxtCosts: A Single Cost

MxtCosts takes one Cost: it either answers "could this be paid here" or pays it in one go. For several entries use MxtResources, which simulates the whole array before ordered deductions. Separate MxtCosts.consume calls check independently and do not share a preflight pass.

Methods

Method	Parameters	Return value	Description
check(player, definition)	Player, any of the five Cost shapes	boolean	Only answers "could this be paid here": it is read-only and changes no inventory, value or aura, so a client script may call it.
consume(player, definition)	Player, any of the five Cost shapes	boolean	A simulation refusal returns false without deduction. Once simulation passes, a real failure or runtime exception only logs WARN and still returns true, without rollback. Server-only: on a client script it logs one warning and returns false without touching the player.
register(id, check, consume)	Callback ID, (player, params, context) => boolean, (player, params, context) => void	void	Registers a script cost. Datapack type: mxt:js.

check and consume take the same Cost shape (the five forms are on Shared Data Types) and go through the same transaction: check is the read-only pre-flight and consume pays in one go.

MxtCosts.register('example:quest_token',
  (player, params, context) => {
    const needed = params.count || 1
    return player.persistentData.getInt('tokens') >= needed
  },
  (player, params, context) => {
    const needed = params.count || 1
    player.persistentData.putInt('tokens', player.persistentData.getInt('tokens') - needed)
  }
)

{"type": "mxt:js", "id": "example:quest_token", "params": {"count": 3}}

A script cost needs a player and keeps its position in the cost array. Check must be read-only; consume failures are not refunded and do not cancel later fees or business effects. A Cost is checked with the payer alone, so the context a cost callback receives is built from that payer and carries no event payload; context.value('level') works, context.value('damage') does not.

Full cost registry dispatch is supported. The current built-in types:

// Spend a value. Typed cost form.
{ type: 'mxt:resource', resource: 'mxt:spirit_power', amount: 10 }

// Spend a value. The id shorthand, accepted by MxtCosts and by MxtResources.consume.
{ id: 'mxt:spirit_power', amount: 10 }

// Spend an aura. It charges the value that aura is measured in.
{ type: 'mxt:aura', aura: 'mxt:fire_aura', amount: 2 }

// Spend items. items accepts an item ID, an item tag, or an ItemMatcher object.
{ type: 'mxt:item', items: ['minecraft:emerald', '#c:mystic_gems'], amount: 2 }

// Delegate to a script. id is the callback registered with MxtCosts.register.
{ type: 'mxt:js', id: 'example:quest_token', params: { count: 3 } }

Related

• Several entries paid in one go: MxtResources.
• The Cost shapes and which channel each is charged to: Shared Data Types.
• KubeJS API Reference.