[Datastar](https://data-star.dev) updates HTML and reactive signals from server responses. Use `data-*` attributes to bind signals to elements and actions such as `@get` to send requests.
Topcoat extracts signals from requests and creates Datastar responses. Return one update from a handler or send several over a [server-sent event stream](crate::router::content::sse).
Everything below is re-exported from `topcoat::datastar` and gated behind the `datastar` feature, which also enables the router's `sse` feature.
```toml
# Cargo.toml
[dependencies]
topcoat = { version = "0.11.0", features = ["datastar"] }
```
# Loading the Datastar script
Load the Datastar script before using its attributes. This example bundles the script as a Topcoat asset:
```rust
use topcoat::{
Result,
asset::asset,
router::{Slot, layout},
view::{View, view},
};
#[layout]
async fn root(slot: Slot<'_>) -> Result<impl View> {
Ok(view! {
<!DOCTYPE html>
<html>
<head>
<script
type="module"
src=(asset!("https://cdn.jsdelivr.net/gh/starfederation/datastar@1.0.2/bundles/datastar.js"))
></script>
</head>
<body>(slot)</body>
</html>
})
}
```
See the [assets guide](crate::asset) for loading the asset bundle on your router.
# Reading signals
The [`Signals`] extractor deserializes request signals into your type. It reads JSON from the `datastar` query parameter for GET requests and from the body for other methods.
```rust
// src/app/increment.rs
use serde::{Deserialize, Serialize};
use topcoat::{
Result,
datastar::{PatchSignals, Signals},
router::route,
};
#[derive(Deserialize, Serialize)]
struct Counter {
count: u64,
}
#[route(POST)]
async fn increment(Signals(counter): Signals<Counter>) -> Result<PatchSignals> {
PatchSignals::json(&Counter {
count: counter.count + 1,
})
}
```
Use `Option<Signals<T>>` to also accept requests without Datastar. It returns `None` unless `Datastar-Request` is `true`. A Datastar request with malformed signals still returns an error. Use [`datastar_request`] to check the header directly.
# Patching elements
[`PatchElements`] updates page elements with HTML. By default, Datastar matches elements by `id` and morphs them to match the response. Use [`selector`](PatchElements::selector) and [`mode`](PatchElements::mode) to choose another target or update behavior. Returned from a handler, the patch sends one SSE event and closes the stream:
```rust
// src/app/entries.rs
use topcoat::{
Result,
context::Cx,
datastar::{ElementPatchMode, PatchElements},
router::route,
view::{ViewExt, view},
};
#[route(POST)]
async fn create(cx: &Cx) -> Result<PatchElements> {
let entry = view! { cx => <li>"A new entry"</li> }.single().await?;
Ok(PatchElements::new(entry.render(cx))
.selector("#feed")
.mode(ElementPatchMode::Prepend))
}
```
[`PatchElements::remove`] deletes elements matching a selector.
# Patching signals
[`PatchSignals`] merges a JSON object into the browser's signals. Set a value to `null` to remove it, or use [`only_if_missing`](PatchSignals::only_if_missing) to preserve existing values. [`PatchSignals::json`] serializes the object from a `Serialize` value.
# Streaming events
For live updates, return an [`Sse`] stream and convert each patch into an [`Event`] with `Into`. See the [server-sent events guide](crate::router::content::sse) for keep-alives and handling reconnections.
```rust
// src/app/progress.rs
use futures_core::Stream;
use futures_util::stream;
use serde::Serialize;
use topcoat::{
Result,
datastar::PatchSignals,
router::{
content::sse::{Event, KeepAlive, Sse},
route,
},
};
#[derive(Serialize)]
struct Progress {
percent: u8,
}
#[route(GET)]
async fn progress() -> Result<Sse<impl Stream<Item = Result<Event>> + use<>>> {
let events = stream::iter((0..=100u8).step_by(20).map(|percent| {
PatchSignals::json(&Progress { percent }).map(Into::into)
}));
Ok(Sse::new(events).keep_alive(KeepAlive::new()))
}
```
On the page, `data-on:load="@get('/progress')"` subscribes to the stream and applies each event as it arrives.
# Executing scripts
[`ExecuteScript`] appends a `<script>` element to the page. By default, the element removes itself after running.
```rust
use topcoat::datastar::ExecuteScript;
let script = ExecuteScript::new("console.log('saved')");
```
# Plain responses
Datastar also accepts ordinary responses. It patches `text/html` into the page and merges `application/json` into the signals. Response types that implement [`IntoResponseParts`] set headers to control these updates. Place them before the body in a response tuple:
```rust
// src/app/save.rs
use topcoat::{
Result,
context::Cx,
datastar::{DatastarMode, DatastarSelector, ElementPatchMode},
router::route,
view::{ViewExt, ViewHandle, view},
};
#[route(POST)]
async fn save(cx: &Cx) -> Result<(DatastarSelector, DatastarMode, ViewHandle)> {
let status = view! { cx => <p>"Saved!"</p> }.single().await?;
Ok((
DatastarSelector::from("#status"),
DatastarMode(ElementPatchMode::Inner),
status,
))
}
```
# Header constants
The raw `datastar-*` header names are available as `HeaderName` constants in [`topcoat::datastar::header`](crate::datastar::header), for when you want to read or write a header directly.
[`Sse`]: crate::router::content::sse::Sse
[`Event`]: crate::router::content::sse::Event
[`IntoResponseParts`]: crate::router::response::IntoResponseParts