MxtValues: Script Providers

Registering a Script Provider

Method	Callback parameters	Return value	Purpose
number(id, callback)	(context: FormulaContext, params: object)	Finite number	mxt:js number provider.
resourceValue(id, callback)	(holder: ResourceHolderAttachment, resource: Holder<Resource>, context: FormulaContext, params: object)	Finite number	mxt:js resource value provider.

FormulaContext

Every callback that receives a formula context uses the same object: MxtValues.number, MxtValues.resourceValue, and the mxt:js action and condition callbacks. It exposes:

Method	Description
context.value(name)	Reads a variable: an explicit context value first, then the built-in variable registry. A name the context cannot provide is reported — a development environment logs the whole error, production logs one warning line per distinct message — and returns 0.
context.explicit(name)	The explicit value alone, or NaN when the context carries none. Use it to test whether the current event supplied a payload without asking the variable registry.
context.contains(name)	Whether the context can provide the name right now. This never reports anything and never throws.
context.variables()	The explicit values only: event payloads and anything a caller added. Entity and resource variables are read out of the context objects on demand and are not listed here.
context.player()	Returns the current player, or null when there is none.
context.caster()	Returns the acting entity, or null in a context built without one.
context.target()	Returns the second entity of a bi-entity formula, or null.
context.resource()	Returns the cultivation state bound to this evaluation, or null in a formula that is not tied to one resource.
context.random()	Returns the authoritative random source used by this evaluation.

Formula variables are built in: a script can read every name listed in Formula Variables, but it cannot register a new one.

In resourceValue, holder is the resource attachment and resource is the resource holder; they are normally used read-only, for example holder.get(resource). Do not use this callback to write state.

Evaluation

Method	Parameters	Return value	Description
evaluateNumber(entity, definition)	Entity, number provider object	number	Evaluates any registered provider. A non-finite result returns 0.
evaluateResource(entity, resource, definition)	LivingEntity, resource ID, resource value provider JSON	number	Evaluates the value of the given resource. An entity-aware provider reads the environment/actual aura at the current position.

A definition is decoded once per distinct JSON text and then reused, because decoding builds the whole provider tree including its expressions. A script that evaluates the same definition every tick therefore parses it once. The decoded values are dropped when the world's registries change, and a definition a script has edited into a different JSON text is decoded again.

const levelScaled = MxtValues.evaluateNumber(player, {
  type: 'mxt:expression',
  expression: 'level * 2 + 1'
})
const actualAura = MxtValues.evaluateResource(player, 'mxt:spirit_power', {
  type: 'mxt:actual_concentration'
})

Related

• The other two places that receive a FormulaContext: MxtActions and MxtConditions.
• Using a value as a price: MxtCosts and MxtResources.
• Data pack side: Number Provider Types, Formula Variables and Shared Data Types.
• KubeJS API Reference.