Error handling

Every attribute mounts inside its own error boundary. A syntax error, a thrown exception in an event handler, or an effect that fails is reported and the rest of the page keeps mounting and reacting.

createSigmx({
  plugins,
  onError: (error, { plugin, el, attr }) => {
    console.warn(`${attr} on`, el, error)
    telemetry.capture(error, { plugin })
  },
})

The default handler is console.error. Errors thrown by an expression carry the failing source; errors from plugins have a message prefixed with the attribute name, for example data-on: needs a key, e.g. :name.

Common messages

message	cause
needs a key / takes no key / needs a value / takes no value	the directive’s key or value requirement was violated
needs a value / does not take a value	the directive’s value requirement was violated
unknown action @name	the function is not registered; add its plugin
"x" is a computed signal and cannot be assigned	an expression wrote to a data-computed path
effect loop	an effect writes a signal it reads; use @peek or restructure
@get needs a URL	the first argument was empty
no form found	contentType: 'form' outside a form and without selector

Requests

Failed requests do not throw into your markup. They emit sigmx-fetch with type: 'error' and status or message; the retry policy runs quietly, and a finished event follows once it gives up. Listen with data-on:sigmx-fetch__document="…" or from JavaScript.