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Update docs for 3.0 changes.

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Dillon Kearns 2022-11-10 17:18:42 +05:30
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src/DataSource.elm
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@ -7,7 +7,7 @@ module DataSource exposing
, map2, map3, map4, map5, map6, map7, map8, map9
)
{-| In an `elm-pages` app, each page can define a value `data` which is a `DataSource` that will be resolved **before** `init` is called. That means it is also available
{-| In an `elm-pages` app, each Route Module can define a value `data` which is a `DataSource` that will be resolved **before** `init` is called. That means it is also available
when the page's HTML is pre-rendered during the build step. You can also access the resolved data in `head` to use it for the page's SEO meta tags.
A `DataSource` lets you pull in data from:
@ -20,9 +20,17 @@ A `DataSource` lets you pull in data from:
- Or any combination of the above, using `DataSource.map2`, `DataSource.andThen`, or other combining/continuing helpers from this module
## Where Does DataSource Data Come From?
## DataSource's vs. Effect's/Cmd's
Data from a `DataSource` is resolved when you load a page in the `elm-pages` dev server, or when you run `elm-pages build`.
DataSource's are always resolved before the page is rendered and sent to the browser. A DataSource is never executed
in the Browser. Instead, the resolved data from the DataSource is passed down to the Browser - it has been resolved
before any client-side JavaScript ever executes. In the case of a pre-rendered route, this is during the CLI build phase,
and for server-rendered routes its DataSource is resolved on the server.
Effect's/Cmd's are never executed on the CLI or server, they are only executed in the Browser. The data from a Route Module's
`init` function is used to render the initial HTML on the server or build step, but the Effect isn't executed and `update` is never called
before the page is hydrated in the Browser. This gives a deterministic mental model of what the first render will look like,
and a nicely typed way to define the initial `Data` you have to render your initial view.
Because `elm-pages` hydrates into a full Elm single-page app, it does need the data in order to initialize the Elm app.
So why not just get the data the old-fashioned way, with `elm/http`, for example?