URLs

The node id is the URL path. profile.name ⇄ /profile/name. No route table.

import { toPath, toValue } from '@1state/core'

toPath({ profile: 'name' })   // ["profile", "name"]
toValue(['profile', 'name'])  // { profile: "name" }

route(segments)

route(segments) gives a step page everything it needs off one replay of the trail:

await machine.route(['billing', 'card'])  // { target: null, prev: ["profile", "name"] }
await machine.route(['profile', 'name'])  // { target: null, prev: null }
await machine.route(['review'])           // { target: ["billing", "card"], prev: null }

• target — null means allow. Otherwise redirect there. The current step and any earlier one are allowed; that is back-navigation and re-editing. Unknown, off-flow or ahead bounces to current.
• prev — the Back link for the requested step, not for the current one. Re-editing an earlier answer has to go back to what preceded it. null on the first step, and while redirecting.

Change an earlier answer and both change with it, because both come from the same replay.

A step page

The whole contract for a step page is one call.

const machine = createMachine(onboard, { scripts, context: await load(accountId) })
await machine.start()

const { target, prev } = await machine.route(params.segments)
if (target) redirect(302, `/${target.join('/')}`)

render({ step: params.segments, back: prev && `/${prev.join('/')}` })

The redirect is not an access check bolted on top. A step ahead of the current one is unreachable because its predecessors’ guards have not passed, and route() reports that rather than enforcing it.

Never restore from the URL

Never restore from the URL. Do not feed toValue(segments) into options.state. Settling from context is the entire no-skip-ahead guarantee; a typed URL that restores directly walks straight past it.

Build from context, call start(), and ask route() what to do with the requested segments.

Series only

toPath and toValue are series-only, for the same reason path() and back() are: a parallel region has no single predecessor. Give each region its own segments if you need URLs over a parallel state. See Limits.