This is a very basic implementation and doesn't
check that the points are indeed valid.
A proper solution is to request the list of preplots
for that line from the server and validate against those.
It shows a graphical representation of the
acquisition status of a preplot line, as
stacked bars where each bar represents the
acquisition extent of a sequence. This is
complemented by colour denoting the raw/final/
ntbp status of the sequence and by a tooltip
with the same information. Sequence bars may be
made clickable by providing a function to the
"sequence-href" property; this function should
take a sequence object and return a URL.
On the backend, the events endpoint caches responses
by ETag in order to reduce the load on the database
and response times. That cache is supposed to be
invalidated with the middleware receives a notification
that the underlying data has changed. However, that
change might arrive just *after* the HTTP request,
meaning that if we let the browser do its thing we
will probably be returning stale data.
So what we do is we explicitly request a non-cached
response when we know that something has changed
because we changed it ourselves.
What we do not do is bypass the cache if we receive
a change event notification, as we assume that the
HTTP roundtrip will be more than sufficient for
the server to have invalidated (and perhaps even
refreshed) its response.
The callback has the signature (err, res) where
res is the result object from the fetch() request
and err is non-null if an error occurred and fetch()
threw.
The callback is called before res.json() has had a
chance to run it is really not recommended to
consume the body from this callback as this will cause
an error in the API action itself.
