Alert 🚨

Lets write an alert.

A note on using web-sys APIs

We can find the API we need using a search within the web-sys docs:

pub fn alert_with_message(&self, message: &str) -> Result<(), JsValue>

The alert() method

MDN Documentation

This API requires the following crate features to be activated: Window

This last bit about "This API require the following..." is important. web-sys is huuuuuge because it contains a lot of APIs. To cut down on compile times, etc. the authors decided to have each API be opt-in, so you must add that API to your Cargo.toml's features list. Luckily we have a project template that includes this stuff (along with a little note):

version = "0.3"
# Add more web-sys API's as you need them
features = [

To use the Window API we have to add "Window" to the list of features:

features = [

Now we can write our little app:

use wasm_bindgen::prelude::*;
use web_sys::window;

pub fn main() -> Result<(), JsValue> {
  let window = window().unwrap();
  window.alert_with_message("Hello from WASM!")