Hyperapp: A streamlined JavaScript library for building feature-rich web applications

Hyperapp is a lightweight JavaScript library for building feature-rich web applications. It combines a pragmatic, Elm-inspired approach to state management with a VDOM engine that supports keyed updates and lifecycle events—all without relying on other libraries. The source code size after it is minimized and gzip compressed is about 1KB.

This tutorial will introduce you to Hyperapp and help you get started quickly with some code examples. I assume you have some understanding of HTML and JavaScript, but don't need to have experience using other frameworks.

Key Points

• Hyperapp is a compact JavaScript library that allows developers to build web applications that combine state management with a virtual DOM engine, with a size of about 1KB.
• Applications built with Hyperapp consist of a single state object, operations that modify states, and views that convert states and operations into user interfaces. State is a normal JavaScript object that describes the application's data model and is immutable.
• Hyperapp uses a virtual DOM, which is a description of what the actual DOM should look like, created from scratch in each rendering cycle. This brings high efficiency, as there are usually only a few nodes that need to be changed.
• Hyperapp can be used with JSX (a JavaScript language extension for representing dynamic HTML) or alone. You can also load Hyperapp from a CDN like unpkg, which will be available globally via the window.hyperapp object.
• Hyperapp is simpler compared to other libraries like React or Vue because it is small and is a complete solution for building web applications. It further develops the concept of view as a state function and has built-in state management solutions inspired by Elm.

Hello World

We will start with a simple demonstration showing all the components working together. You can also try this code online.

import { h, app } from "hyperapp";
// @jsx h

const state = { count: 0 };

const actions = {
  down: () => state => ({ count: state.count - 1 }),
  up: () => state => ({ count: state.count + 1 })
};

const view = (state, actions) => (
  <div>
    <h1>{state.count}</h1>
    <button onclick={actions.down}>-</button>
    <button onclick={actions.up}>+</button>
  </div>
);

app(state, actions, view, document.body);

This is roughly what each Hyperapp application looks like: a single state object, operation that fills states, and a view that converts states and operations into user interfaces.

Inside the app function, we copy your state and operations (it is impolite to modify objects we don't own) and pass them to the view. We also wrap your actions so that the application is re-rendered every time the state changes.

app(state, actions, view, document.body);

State is a normal JavaScript object that describes your application data model. It is also immutable. To change it, you need to define the actions and call them.

const state = { count: 0 };

In the view, you can display the properties of the state, use it to determine which parts of the UI should be displayed or hidden, etc.

<h1>{state.count}</h1>

You can also attach an action to a DOM event, or call an action in your own inline event handler.

import { h, app } from "hyperapp";
// @jsx h

const state = { count: 0 };

const actions = {
  down: () => state => ({ count: state.count - 1 }),
  up: () => state => ({ count: state.count + 1 })
};

const view = (state, actions) => (
  <div>
    <h1>{state.count}</h1>
    <button onclick={actions.down}>-</button>
    <button onclick={actions.up}>+</button>
  </div>
);

app(state, actions, view, document.body);

The operation will not directly modify the state, but will return a new clip of the state. If you try to modify the state in an action and then return it, the view will not rerender as you expected.

app(state, actions, view, document.body);

app Call returns the operation object connected to the status update-view rendering cycle. You also receive this object in view functions and operations. It is very useful to expose this object to the outside world because it allows you to interact with your application from another program, framework, or native JavaScript.

const state = { count: 0 };

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Summary: Hyperapp provides a lightweight solution for building efficient web applications with its extremely small size and simple design. It provides powerful features in state management and virtual DOM while maintaining easy-to-learn and use features. Whether it is a small project or a large application, Hyperapp can provide an efficient and flexible development experience.

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