App 1: Counter

When you click the button, the number is incremented.

Counter example is the default example in the basic quickstart so you don't have to modify code at all.

The entire code (/src/lib.rs content) without comments and extra items to satisfy linters:

use seed::{prelude::*, *};

fn init(_: Url, _: &mut impl Orders<Msg>) -> Model {
    Model::default()
}

type Model = i32;

enum Msg {
    Increment,
}

fn update(msg: Msg, model: &mut Model, _: &mut impl Orders<Msg>) {
    match msg {
        Msg::Increment => *model += 1,
    }
}

fn view(model: &Model) -> Node<Msg> {
    div![
        C!["counter"],
        "This is a counter: ",
        button![model, ev(Ev::Click, |_| Msg::Increment),],
    ]
}

#[wasm_bindgen(start)]
pub fn start() {
    App::start("app", init, update, view);
}

You'll learn about individual parts (Model, update, etc.) in the next chapters. If you want to zoom out a bit before we'll jump into the rabbit hole, I recommend to read something about The Elm Architecture (TEA).