Context

What

Context is the actor’s mutable data record. Pass it in at construction, read and replace it during the run. It survives transitions.

State decides where the machine is. Context decides what it knows.

Define

import { checkout, type CheckoutContext } from "../checkout.ts";

const c: CheckoutContext = checkout.context;

Typed at compile time. No runtime cost.

Read and write

Handlers get a context handle:

• context.get() returns the live record
• context.set(s) writes it back (any call triggers change, even same reference)
• Mutate what get() returned, then set() it

m.on(basicInfo, submitBasicInfo, (event, { context }) => {
  const s = context.get();
  s.basicInfo = event.payload;
  context.set(s);
  return { state: shippingAddress };
});

Nested mutations work the same way (s.items.push(item); context.set(s)).

Read outside transitions

checkout.context.basicInfo?.email;

Effects

Effects get the same handle. Read, mutate, set(), then emit().

Children

Child actors (regions) have their own context. They communicate via events. See States.