Trait JsCast 

pub trait JsCast:
    Sized
    + AsRef<JsValue>
    + Into<JsValue> {
    // Required methods
    fn instanceof(val: &JsValue) -> bool;
    fn unchecked_from_js(val: JsValue) -> Self;
    fn unchecked_from_js_ref(val: &JsValue) -> &Self;

    // Provided methods
    fn is_type_of(val: &JsValue) -> bool { ... }
    fn has_type<T>(&self) -> bool
       where T: JsCast { ... }
    fn dyn_into<T>(self) -> Result<T, Self>
       where T: JsCast { ... }
    fn dyn_ref<T>(&self) -> Option<&T>
       where T: JsCast { ... }
    fn is_instance_of<T>(&self) -> bool
       where T: JsCast { ... }
    fn unchecked_into<T>(self) -> T
       where T: JsCast { ... }
    fn unchecked_ref<T>(&self) -> &T
       where T: JsCast { ... }
}

Trait for types that can be cast to and from JsValue.

This is the wry-bindgen equivalent of wasm-bindgen’s JsCast trait. It enables safe and unsafe casting between JavaScript types.

Required Methods

fn instanceof(val: &JsValue) -> bool

Check if a JsValue is an instance of this type.

This performs a runtime instanceof check in JavaScript.

fn unchecked_from_js(val: JsValue) -> Self

Unchecked cast from JsValue to this type.

Safety

This does not perform any runtime checks. The caller must ensure the value is actually of the correct type.

fn unchecked_from_js_ref(val: &JsValue) -> &Self

Unchecked cast from a JsValue reference to a reference of this type.

Safety

This does not perform any runtime checks. The caller must ensure the value is actually of the correct type.

Provided Methods

fn is_type_of(val: &JsValue) -> bool

Performs a dynamic type check to see whether the JsValue provided is a value of this type.

Unlike instanceof, this can be specialized to check for primitive types or perform other type checks that aren’t possible with instanceof. The default implementation falls back to instanceof.

fn has_type<T>(&self) -> bool

where T: JsCast,

Test whether this JS value has a type T.

This method will dynamically check to see if this JS object can be casted to the JS object of type T. Usually this uses the instanceof operator, but can be customized with is_type_of. This also works with primitive types like booleans/strings/numbers as well as cross-realm objects like Array which can originate from other iframes.

In general this is intended to be a more robust version of is_instance_of, but if you want strictly the instanceof operator it’s recommended to use that instead.

fn dyn_into<T>(self) -> Result<T, Self>

where T: JsCast,

Try to cast this value to type T.

Returns Ok(T) if the value is an instance of T, otherwise returns Err(self) with the original value.

fn dyn_ref<T>(&self) -> Option<&T>

where T: JsCast,

Try to get a reference to type T from this value.

Returns Some(&T) if the value is an instance of T, otherwise returns None.

fn is_instance_of<T>(&self) -> bool

where T: JsCast,

Test whether this JS value is an instance of the type T.

This method performs a dynamic check (at runtime) using the JS instanceof operator. This method returns self instanceof T.

Note that instanceof does not always work with primitive values or across different realms (e.g. iframes). If you’re not sure whether you specifically need only instanceof it’s recommended to use has_type instead.

fn unchecked_into<T>(self) -> T

where T: JsCast,

Unchecked cast to another type.

fn unchecked_ref<T>(&self) -> &T

where T: JsCast,

Unchecked cast to a reference of another type.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementors

impl JsCast for JsError

impl JsCast for JsValue

Implement JsCast for JsValue itself (identity cast)