dioxus-web-component-macro

Provide a proc macro to build Dioxus web component.

Example

The macro replaces the Dioxus #[component] macro.

use dioxus::prelude::*;
use dioxus_web_component::{web_component, DioxusWebComponent};
use wasm_bindgen::prelude::*;

#[web_component]
fn MyWebComponent(
  attr: Option<String>,
  event: EventHandler<i64>,
) -> Element {
  rsx ! {
    div {
      // ...
    }
  }
}

#[wasm_bindgen(main)]
pub fn main() {
  // Register the web component (aka custom element)
  register_my_web_component();
}

<!-- include the script generated with wasm-pack -->
<script type="module" src="my-web-component.js"></script>

<!-- in the body -->
<my-web-component attr="plop"></my-web-component>

Usage

Tag

The custom element tag is built from the component name.

By default, the tag is the kebab-case version of the name. For example, MyWebComponent becomes my-web-component.

You can change the default behavior with the tag attribute.

use dioxus::prelude::*;
use dioxus_web_component::{web_component, DioxusWebComponent};

#[web_component(tag = "plop-component")]
fn MyWebComponent(
  // ...
) -> Element { todo!() }

<!-- in the body -->
<plop-component></plop-component>

ℹ️ INFO: the custom element tag name has constraints. The macro checks the validity of the tag for you. See MDN - Valid custom element names

Style

You can provide the web component style with the style attribute.

use dioxus::prelude::*;
use dioxus_web_component::{web_component, InjectedStyle};

#[web_component(
  tag = "plop-greeting", 
  style = InjectedStyle::css(include_str!("./style.css"))
)]
fn Greeting(
  // ...
) -> Element {
  todo!()
}

The dioxus_web_component::InjectedStyle could be raw CSS included in an HTML <style>...</style> element, or a link to an external stylesheet, or a list of InjectedStyle styles.

⚠️ WARNING: the web component is wrapped into an HTML div with the dioxus CSS class.

Component parameters

Every parameter of your component should be an attribute, a property, or an event. Note that a parameter could be both an attribute and a property.

The proc macro tries to detect the kind of parameter by looking at its type. If the type starts by EventHandler it is expected to be an event. But, this kind of detection is not reliable, so you might need to add an annotation to correct this behavior.

The annotations are also required if you need to customize the behavior.

Attributes

Attributes are like the href of an <a> HTML element.

You can enforce the parameter to be an attribute with the #[attribute] annotation.

When the attribute value changes the dioxus component will be rendered.

The HTML value of an attribute is a String, so you should be able to parse that string into the target type.

Attribute name

The attribute name is by default the kebab-case of the parameter name. You can choose another name with #[attribute(name = "my-custom-name")].

Attribute option

The attribute could be optional or not. The proc macro tries to detect it automatically with the type name. However the detection is not reliable, so you can use the #[attribute(option = true)] to fix the detection if necessary.

Attribute initial

Attributes require to have an initial value. This value is used when no HTML attribute is provided, or if the attribute is removed.

By default, we expect the attribute type to implement std::default::Default. If it's not the case, or if you want to use another value for your attribute you can provide your default expression with #[attribute(initial = String::from("World"))].

Note that Option<T> implements Default with the None value even if T does not implement itself Default.

Attribute parse

HTML attributes are strings and optional, so we need to convert the attribute value into the component parameter type.

The proc macro uses the std::str::parse method. That means the target type needs to implement the std::str::FromStr trait.

In case of an error, the initial value (see below) is used.

If you want to change this behavior, you can provide your parsing expression.

If the parameter type is optional, the parse expression is used in this code: let value = new_value.and_then(#parse);. If the type is NOT optional, the code looks like let value = new_value.and_then(#parse).unwrap_or_else(|| #initial);.

The expected type for the parsing expression is FnOnce(String) -> Option<T>. The default expression is |value| value.parse().ok().

For example, if you have a parameter required of type bool and you want the value to be true if the attribute is present whatever the content of the attribute, you could use #[attribute(parse = |s| !s.is_empty() )].

Property

On the Rust side of the code, properties work like attributes. The property is not accessible with pure HTML, you need Javascript to get/set the property.

Instead of the String representation, you need to be able to convert the Rust type into a Javascript type (here a wasm_bindgen::JsValue). For the setter, you need the opposite conversion.

Attribute name

The attribute name is by default the camelCase of the parameter name. You can choose another name with #[property(name = "valueAsDate")].

Attribute readonly

If true, it avoids setting the property from the javascript side. By default getter and setter are generated.

Attribute initial

Properties require to have an initial value. This value is used when the component is initialized.

By default, we expect the property type to implement std::default::Default. If it's not the case, or if you want to use another value for your property you can provide your default expression with #[property(initial = String::from("World"))].

Attribute try_into_js

For the getter, the property value should be converted to a wasm_bindgen::JsValue. By default, we use the std::convert::TryInto implementation.

Note that there are many ways to implement TryInto<JsValue>, for example with impl TryFrom<T> for JsValue or even impl From<T> for JsValue. See Rust TryInto.

You can provide your custom conversion into the JsValue with the try_into_js attribute. The expected type for the parsing expression is FnOnce(T) -> Result<JsValue, _>. Not that we do not care about the error type because the error case is ignored and returns undefined.

The default expression is |value| value.try_into().

Example to convert a custom type that wraps a bool:

// ...
#[property(
    try_into_js = |prop| {
        let js_value = if prop.0 {
            JsValue::TRUE
        } else {
            JsValue::FALSE
        };
        Ok::<_, Infallible>(js_value)
    },
)]
prop2: MyProp,
// ...

#[derive(Clone, PartialEq, Default)]
struct MyProp(bool);

But in that situation, the recommended way is to implement From<MyProp> for JsValue.

Attribute try_from_js

For the setter, the property value should be converted from a wasm_bindgen::JsValue. By default, we use the std::convert::TryInto implementation.

Note that there are many ways to implement TryInto<T>, for example with impl TryFrom<JsValue> for T or even impl From<JsValue> for T. See Rust TryInto.

You can provide your custom conversion from the JsValue with the try_from_js attribute. The expected type for the parsing expression is FnOnce(JsValue) -> Result<T, _>. Not that we do not care about the error type because the error case is ignored.

The default expression is |value| value.try_into().

Example to convert a custom type that wraps a bool:

// ...
#[property(
    try_from_js= |value| Ok::<_, Infallible>(MyProp(value.is_truthy())),
)]
prop2: MyProp,
// ...

#[derive(Clone, PartialEq, Default)]
struct MyProp(bool);

But in that situation, the recommended way is to implement From<JsValue> for MyProp.

Events

The web component could send custom events. If the type of the component parameter is EventHandler, the parameter is detected as an event. Because this detection is not reliable, you could enforce a parameter to be an event with the #[event] annotation.

The custom event detail corresponds to the generic type of the Dioxus EventHandler.

⚠️ IMPORTANT: The event type needs to implement Into<JsValue> and be 'static (does not have any reference).

You may need to implement it manually. You could use serde-wasm-bindgen, gloo_utils::format::JsValueSerdeExt, wasm_bindgen::UnwrapThrowExt to implement the Into<JsValue> trait.

Event name

The HTML event name is detected from the parameter name by removing the on_ (or on) prefix and converting the name to kebab-case. You can choose your value with the name attribute like #[event(name = "build")] to dispatch a build event.

Event no_bubble

By default, the event bubbles up through the DOM. You can avoid the bubbling with #[event(no_bubble = true)].

Event no_cancel

By default, the event is cancelable. You can avoid the bubbling with #[event(no_cancel = true)].