web-sys
Inheritance between JS classes is the bread and butter of how the DOM works on the web, and as a result it's quite important for web-sys
to provide access to this inheritance hierarchy as well! There are few ways you can access the inheritance hierarchy when using web-sys
.
Deref
Like smart pointers in Rust, all types in web_sys
implement Deref
to their parent JS class. This means, for example, if you have a web_sys::Element
you can create a web_sys::Node
from that implicitly:
let element: &Element = ...; element.append_child(..); // call a method on `Node` method_expecting_a_node(&element); // coerce to `&Node` implicitly let node: &Node = &element; // explicitly coerce to `&Node`
Using Deref
allows ergonomic transitioning up the inheritance hierarchy to the parent class and beyond, giving you access to all the methods using the .
operator.
AsRef
In addition to Deref
, the AsRef
trait is implemented for all types in web_sys
for all types in the inheritance hierarchy. For example for the HtmlAnchorElement
type you'll find:
impl AsRef<HtmlElement> for HtmlAnchorElement impl AsRef<Element> for HtmlAnchorElement impl AsRef<Node> for HtmlAnchorElement impl AsRef<EventTarget> for HtmlAnchorElement impl AsRef<Object> for HtmlAnchorElement impl AsRef<JsValue> for HtmlAnchorElement
You can use .as_ref()
to explicitly get a reference to any parent class from from a type in web_sys
. Note that because of the number of AsRef
implementations you'll likely need to have type inference guidance as well.
JsCast
Finally the wasm_bindgen::JsCast
trait can be used to implement all manner of casts between types. It supports static unchecked casts between types as well as dynamic runtime-checked casts (using instanceof
) between types.
More documentation about this can be found on the trait itself