BackendTask.Http requests are an alternative to doing Elm HTTP requests the traditional way using the elm/http package.
The key differences are:
BackendTask.Http.Requests are performed once at build time (Http.Requests are performed at runtime, at whenever point you perform them)BackendTask.Http.Requests have a built-in BackendTask.andThen that allows you to perform follow-up requests without using tasksIf you need data that is refreshed often you may want to do a traditional HTTP request with the elm/http package.
The kinds of situations that are served well by static HTTP are with data that updates moderately frequently or infrequently (or never).
A common pattern is to trigger a new build when data changes. Many JAMstack services
allow you to send a WebHook to your host (for example, Netlify is a good static file host that supports triggering builds with webhooks). So
you may want to have your site rebuild everytime your calendar feed has an event added, or whenever a page or article is added
or updated on a CMS service like Contentful.
In scenarios like this, you can serve data that is just as up-to-date as it would be using elm/http, but you get the performance
gains of using BackendTask.Http.Requests as well as the simplicity and robustness that comes with it. Read more about these benefits
in this article introducing BackendTask.Http requests and some concepts around it.
A simplified helper around BackendTask.Http.request, which builds up a BackendTask.Http GET request.
import BackendTask
import BackendTask.Http
import Json.Decode as Decode exposing (Decoder)
getRequest : BackendTask Int
getRequest =
BackendTask.Http.get
"https://api.github.com/repos/dillonkearns/elm-pages"
(Decode.field "stargazers_count" Decode.int)
Analogous to the Expect type in the elm/http package. This represents how you will process the data that comes
back in your BackendTask.Http request.
You can derive ExpectJson from ExpectString. Or you could build your own helper to process the String
as XML, for example, or give an elm-pages build error if the response can't be parsed as XML.
Gives the HTTP response body as a raw String.
import BackendTask exposing (BackendTask)
import BackendTask.Http
request : BackendTask String
request =
BackendTask.Http.request
{ url = "https://example.com/file.txt"
, method = "GET"
, headers = []
, body = BackendTask.Http.emptyBody
}
BackendTask.Http.expectString
Handle the incoming response as JSON and don't optimize the asset and strip out unused values.
Be sure to use the BackendTask.Http.request function if you want an optimized request that
strips out unused JSON to optimize your asset size. This function makes sense to use for things like a GraphQL request
where the JSON payload is already trimmed down to the data you explicitly requested.
If the function you pass to expectString yields an Err, then you will get a build error that will
fail your elm-pages build and print out the String from the Err.
The way you build a body is analogous to the elm/http package. Currently, only emptyBody and
stringBody are supported. If you have a use case that calls for a different body type, please open a Github issue
and describe your use case!
A body for a BackendTask.Http request.
Build an empty body for a BackendTask.Http request. See elm/http's Http.emptyBody.
Builds a string body for a BackendTask.Http request. See elm/http's Http.stringBody.
Note from the elm/http docs:
The first argument is a MIME type of the body. Some servers are strict about this!
Builds a JSON body for a BackendTask.Http request. See elm/http's Http.jsonBody.
Build a body from Bytes for a BackendTask.Http request. See elm/http's Http.bytesBody.
elm-pages performs GET requests using a local HTTP cache by default.
Perform a GET request, with some additional options for the HTTP request, including options for caching behavior.