XState.js How to send context to a machine? - xstate

Question

I am new to XState.js.
I want to use a simple ID in my context. How do I update the context using machine.send()?
const fetchMachine = Machine(
{
id: 'test',
initial: 'init',
context: {
id: '',
},
states: {
init: {
on: {
LOGIN: 'fetch',
},
},
fetch: {
on: {
LOGOUT: 'init',
},
},
}
})
const machine = interpret(fetchMachine).start()
How do I pass an ID to the context?
This does NOT do the trick:
machine.send({ type: 'LOGIN', id })

Answer 1

You have to use the assign action to update the context. I've updated your example to the following:
import { Machine, assign } from 'xstate';
// Action to assign the context id
const assignId = assign({
id: (context, event) => event.id
});
export const testMachine = Machine(
{
id: 'test',
initial: 'init',
context: {
id: '',
},
states: {
init: {
on: {
LOGIN: {
target: 'fetch',
actions: [
assignId
]
}
},
},
fetch: {
on: {
LOGOUT: 'init',
},
},
}
},
{
actions: { assignId }
}
);
Now once you call the following:
import { testMachine } from './machines';
const testService = interpret(testMachine).start();
testService.send({type: 'LOGIN', id: 'test' });
//or testService.send('LOGIN', { id: 'test'});
the action assignId will assign data from the event to your context