---
title: 'Build a sample app'
---

First, create a new cargo project:

```bash
cargo new yew-app
```

Open the newly created directory.

First, let's add `yew` as a dependencies in the `Cargo.toml` file:

```toml
[package]
name = "yew-app"
version = "0.1.0"
edition = "2018"

[dependencies]
# you can check the latest version here: https://crates.io/crates/yew
yew = "0.18"
```

Copy the following template into your `src/main.rs` file:

```rust
use yew::prelude::*;

enum Msg {
    AddOne,
}

struct Model {
    // `ComponentLink` is like a reference to a component.
    // It can be used to send messages to the component
    link: ComponentLink<Self>,
    value: i64,
}

impl Component for Model {
    type Message = Msg;
    type Properties = ();

    fn create(_props: Self::Properties, link: ComponentLink<Self>) -> Self {
        Self {
            link,
            value: 0,
        }
    }

    fn update(&mut self, msg: Self::Message) -> ShouldRender {
        match msg {
            Msg::AddOne => {
                self.value += 1;
                // the value has changed so we need to
                // re-render for it to appear on the page
                true
            }
        }
    }

    fn change(&mut self, _props: Self::Properties) -> ShouldRender {
        // Should only return "true" if new properties are different to
        // previously received properties.
        // This component has no properties so we will always return "false".
        false
    }

    fn view(&self) -> Html {
        html! {
            <div>
                <button onclick=self.link.callback(|_| Msg::AddOne)>{ "+1" }</button>
                <p>{ self.value }</p>
            </div>
        }
    }
}

fn main() {
    yew::start_app::<Model>();
}
```

This template sets up your root `Component`, called `Model` which shows a button that updates itself when you click it.
Take special note of `yew::start_app::<Model>()` inside `main()` which starts your app and mounts it to the page's `<body>` tag.
If you would like to start your application with any dynamic properties, you can instead use `yew::start_app_with_props::<Model>(..)`.

Finally, add an `index.html` file in the root directory of your app:

```html
<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8" />
        <title>Yew App</title>
    </head>
</html>
```

## Run your app

If you haven't already, install [Trunk](https://github.com/thedodd/trunk):

```bash
cargo install trunk wasm-bindgen-cli
```

If you haven't already installed it, you need to add the `wasm32-unknown-unknown` target.
To install this with Rustup:

```bash
rustup target add wasm32-unknown-unknown
```

Now all you have to do is run the following:

```bash
trunk serve
```

This will start a development server which continually updates the app every time you change something.

## Troubleshooting

-   Trunk's installation failed:

    Make sure you have the development packages of openssl installed.
    For example, libssl-dev on Ubuntu or openssl-devel on Fedora.
