dioxus-use-js

A macro that generates Rust bindings to JavaScript or TypeScript functions and classes, with compile time checks. For use with Dioxus. No need to use eval directly anymore! Works across all eval supported platforms (Web, Desktop, Mobile, and liveview) — no wasm-bindgen required.

JavaScript Usage

You can write plain JavaScript and bind exported functions directly.

// assets/example.js

export function greeting(from, to) {
    return `Hello ${to}, this is ${from} speaking from JavaScript!`;
}

Bind it in Rust:

use dioxus_use_js::use_js;

use_js!("assets/example.js"::greeting);

Generated Rust signature:

async fn greeting<T: DeserializeOwned>(from: impl Serialize, to: impl Serialize) -> Result<T, JsError>;

Use it like:

let val: String = greeting("Alice", "Bob").await?;

TypeScript Usage

If you use TypeScript, the macro will parse types to produce more accurate Rust bindings. See the Type Mapping section for details on how TypeScript types are mapped to Rust types.

// js-utils/example.ts

export function greeting(from: string, to: string): string {
    return `Hello ${to}, this is ${from} speaking from JavaScript!`;
}

Build with:

bun build js-utils/example.ts --outfile assets/example.js

See BunBuild for use in build.rs as well - Example

Bind with:

use_js!("js-utils/example.ts", "assets/example.js"::{greeting});

Generated Rust signature:

async fn greeting(from: &str, to: &str) -> Result<String, JsError>;

Macro Syntax

Js

use_js!("bundle.js"::function);
use_js!("bundle.js"::{func1, func2});
use_js!("bundle.js"::*);

Ts

use_js!("source.ts", "bundle.js"::function);
use_js!("source.ts", "bundle.js"::{func1, func2});
use_js!("source.ts", "bundle.js"::*);

Type Mapping

Built-in TypeScript Types

Special Types

Special Types

Special types are types not included in the regular Typescript type system, but are understood by the use_js! macro and may augment the generated binding code.

Json

Json is a simple type that represents valid json. This type can best nested.

type Json = string | number | boolean | null | { [key: string]: Json } | Json[];

Example Usage

TypeScript:

type Json = string | number | boolean | null | { [key: string]: Json } | Json[];

export function json(): Json[] {
    return [
        {"key": "value"},
        {"key": "value"},
    ];
}

Generated Rust signature:

pub async fn json() -> Result<Vec<Value> ,JsError>;

JsValue: Javascript References

This special TypeScript type signals to the macro to bypass serialization and pass native JS values as opaque references between Rust and JavaScript. The macro generates the glue code required. The JS value is automatically disposed when all references on the Rust side go out of scope. Only the following are valid representations:

type JsValue<T = any> = T;

Example Usage

TypeScript:

type JsValue<T = any> = T;

type MyObject = {
    name: string;
    method: (value: number) => number;
};

export function createJsObject(): JsValue<MyObject> {
    return {
        name: "example",
        method: function (value) {
            return value + 25;
        },
    };
}

export function useJsObject(value: JsValue<MyObject>): number {
    let result = value.method(2);
    return result;
}

Generated Rust signature:

pub async fn createJsObject() -> Result<JsValue, JsError>;

pub async fn useJsObject(value: &JsValue) -> Result<f64, JsError>;

Usage:

let js_value_example: Resource<Result<f64, JsError>> = use_resource(|| async move {
    // No serialization!
    // The value is kept on the js side and a reference to it is kept on the rust side.
    // The value is automatically disposed when all rust references no longer exist.
    let js_value = createJsObject().await?;
    let output = useJsObject(&js_value).await?;
    // Since `js_value` is dropped here and all references no longer exist,
    // the referenced value will be disposed on the js side.
    Ok(output)
});

RustCallback: Passing Closures from Rust to JavaScript

This special TypeScript type signals to the macro that a Rust async callback will be passed into the JavaScript function. The macro generates the glue code required. This enables advanced interop patterns, such as calling Rust logic from within JS — all while preserving type safety. This type cannot be nested.

type RustCallback<A, R> = (arg: A) => Promise<R>;

A and R can only be:

• string
• number
• boolean
• T | null
• T[]
• Map<T, TT>
• Set<T>
• void
• Json

Multiple invocations of a RustCallback can be inflight at the same time e.g.

let results = await Promise.all([callback(1), callback(2)]);

Depending on the rust logic (e.g. different network requests), some invocations may finish before others. They do not debounce, wait for finish, or cancel previous requests. If this is desired, one would have to implement this logic themselves. Therefore it may be best to wait for the previous response to finish e.g.

let result1 = await callback(1);
let result2 = await callback(2);

The lifecycle of a RustCallback is tied to the lifecycle of the component the function was called in. i.e when the component drops all ongoing requests will be canceled on the rust side and awaiting promises on the js side will throw notifying that the component has been dropped. Any additional calls to the callback on the js side will also throw.

Since the lifecycle of RustCallback is not tied to the function invocation. The function can return and all RustCallback's will function until the component is dropped.

On the rust side, if the callback returns an Err then the js Promise will be rejected with that serialized value.

Example Usage

TypeScript:

type RustCallback<A, R> = (arg: A) => Promise<R>;

export async function useCallback(
  startingValue: number,
  doubleIt: RustCallback<number, number>
): Promise<number> {
  let doubledValue = await doubleIt(startingValue); // Calls back into Rust
  return doubledValue;
}

Generated Rust signature:

pub async fn useCallback(
    startingValue: f64,
    doubleIt: Callback<f64, impl Future<Output = Result<f64, Value>> + 'static>,
) -> Result<f64, JsError>;

Usage:

// Rust async closure that will be called by JS
let cb = use_callback(move |value: f64| async move {
    Ok(value * 2.0)
});
let callback_example: Resource<Result<f64, JsError>> = use_resource(|| async move {
    // Pass it into the JS function
    let value = useCallback(2.0, callback).await?;
    Ok(value)
});

Drop: Hook Into The Component Drop LifeCycle

Drop is used to hook into the component drop lifecycle on the js side.

type Drop = Promise<void>;

When the promise completes, the component the function was invoked from has been dropped. As such, all RustCallback parameters will now throw if invoked. Therefore, Drop can be used to remove any handlers (e.g. drop.then(() => document.removeEventListener('click', handler))) or abort early from a function invocation.

Drop is different from all the other special types in that it does not rely on any external context provided by user of the function containing it. Therefore, no user facing rust code will be generated for it.

Drop is also available in plain js. Any function parameter named drop without a type will be treated as Drop.

Example Usage

TypeScript:

type Drop = Promise<void>;

export async function dropExample(
  value: number,
  drop: Drop
): Promise<number>;

Generated Rust signature:

pub async fn dropExample(
    value: f64,
) -> Result<f64, JsError>;

Classes

Classes are built on top of JsValue and also supported. e.g.

TypeScript:

/**
 * Class test
 */
export class Counter {
    private count: number;
    private log: RustCallback<string, void>;

    constructor(initialValue: number) {
        this.count = initialValue;
        this.log = async (value) => console.info(value);
    }

    /**
     * Static factory method
     */
    static createDefault(): JsValue<Counter> {
        return new Counter(0);
    }

    /**
     * Static method to add two numbers
     */
    static add(a: number, b: number): number {
        return a + b;
    }

    /**
     * Get the current count
     */
    getCount(): number {
        return this.count;
    }

    /**
     * Increment the counter by a value
     */
    increment(value: number): number {
        this.count += value;
        this.log(`Incremented by ${value}`);
        this.log(`New count is ${this.count}`);
        return this.count;
    }

    /**
     * If set logs every increment on the rust side
     */
    setLog(log: RustCallback<string, void>): void {
        this.log = log;
    }

    /**
     * Async method to double the count
     */
    async doubleAsync(): Promise<number> {
        this.count *= 2;
        return this.count;
    }
}

Generated Rust:

#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub struct Counter(dioxus_use_js::JsValue);

impl Counter {
    pub fn new(js_value: dioxus_use_js::JsValue) -> Self {
        Self(js_value)
    }
}
impl Counter {
    #[doc = " Static factory method"]
    pub async fn createDefault() -> Result<Counter, dioxus_use_js::JsError> {
        unimplemented!("Removed for the example");
    }
    #[doc = " Static method to add two numbers"]
    pub async fn add(a: f64, b: f64) -> Result<f64, dioxus_use_js::JsError> {
        unimplemented!("Removed for the example");
    }
    #[doc = " Get the current count"]
    pub async fn getCount(&self) -> Result<f64, dioxus_use_js::JsError> {
        unimplemented!("Removed for the example");
    }
    #[doc = " Increment the counter by a value"]
    pub async fn increment(&self, value: f64) -> Result<f64, dioxus_use_js::JsError> {
        unimplemented!("Removed for the example");
    }
    #[doc = " If set logs every increment on the rust side"]
    pub async fn setLog(
        &self,
        log: dioxus::core::Callback<
            String,
            impl Future<Output = Result<(), dioxus_use_js::SerdeJsonValue>> + 'static,
        >,
    ) -> Result<(), dioxus_use_js::JsError> {
        unimplemented!("Removed for the example");
    }
    #[doc = " Async method to double the count"]
    pub async fn doubleAsync(&self) -> Result<f64, dioxus_use_js::JsError> {
        unimplemented!("Removed for the example");
    }
}
impl AsRef<dioxus_use_js::JsValue> for Counter {
    fn as_ref(&self) -> &dioxus_use_js::JsValue {
        &self.0
    }
}