6 · Weather

weather.weather — weather.clj, weather_controller.clj, weather_api.clj.

An :invoke that calls a public API (Open-Meteo, no key), and the two loading patterns you will use everywhere.

State machine

stateDiagram-v2
  direction LR
  [*] --> loading : INIT / seed
  loading --> fetching : LOAD
  fetching --> loaded : fetch-weather! ok / keep weather
  fetching --> failed : fetch-weather! failed / keep error
  loaded --> fetching : SEARCH / capture city
  failed --> fetching : SEARCH / capture city
  failed --> fetching : LOAD

The lazy load. Invokes run synchronously inside the request, so a fetch in INIT would hold the first paint. Instead INIT renders a skeleton (:loading) whose data-init posts LOAD at once; LOAD enters :fetching, whose invoke does the slow work, and the response replaces the skeleton with :loaded or :failed. Two requests, instant first paint. Any component that loads something expensive on open should look like this.

The in-flight indicator. The search buttons carry data-indicator="_weatherBusy": Datastar sets $_weatherBusy true while their request is pending, so data-show on the spinner and data-attr:disabled on the buttons work without the server knowing. The leading underscore makes the signal Datastar-local; it never rides along to the server.

Where the data lives. The city — the user's choice — is in :memory (bound to the input). The weather and the error are in top-level ctx: derived data, re-fetched on demand, never echoed back from the client. The retry in :failed is a plain LOAD and INIT is machine-wide, so a reconnect re-fetches from any state.

Capture before invoke. The quick picks post search?city=Oslo; the invoke cannot see event params, so capture-city stores it in :memory in the transition's :actions and fetch-weather! reads it from there.

Errors as data. weather-api throws ex-info with a user-facing :message for an unknown place or a failing service; :on-error puts it in ctx and the render shows it.

Try it: bb dev, open the weather page (?example=weather on the URL it prints), type a city, try a nonsense one. The e2e run sets TAIA_EXAMPLES_FAKE_WEATHER=1, which answers four cities from a table after 700 ms instead of calling the network.

Spec: block 6 in examples_test.clj (the API is redefined with a spy: INIT does not fetch, LOAD fetches once with the city, SEARCH captures the param first, the error path) and e2e/tests/weather.spec.ts (skeleton first, indicator during a search, recovery from :failed).