Hello, Rust!

Demo: Call JavaScript from Rust

Click the button to run the WebAssembly code.

Run

---

The Code

Download call-js.rs
Download call-js.wat (WebAssembly text format)

extern {
    fn alert(ptr: *const u8, number: u32);
}

#[no_mangle]
pub extern "C" fn run() {
    unsafe {
        let x = b"Hello World!\0";
        alert(x as *const u8, 42);
    }
}

The JavaScript code loads the WebAssembly module and has access to the exported function.

window.Module = {};

const imports = {
  env: {
    alert: function(ptr, number) {
      let str = copyCStr(Module, ptr);
      alert(str + " -> " + number);
    }
  }
};

fetchAndInstantiate("./call-js.wasm", imports)
.then(mod => {
  Module.memory      = mod.exports.memory;
  Module.run         = mod.exports.run;
  Module.dealloc_str = function() {}

  Module.run();
});