Friday, 8 June, 2018 UTC


Summary

In this tutorial, we’ll be using Hyperapp to build a to-do list app. If you want to learn functional programming principles, but not get bogged down in details, read on.
Hyperapp is hot right now. It recently surpassed 11,000 stars on GitHub and made the 5th place in the Front-end Framework section of the 2017 JavaScript Rising Stars. It was also featured on SitePoint recently, when it hit version 1.0.
The reason for Hyperapp’s popularity can be attributed to its pragmatism and ultralight size (1.4 kB), while at the same time achieving results similar to React and Redux out of the box.
So, What Is HyperApp?
Hyperapp allows you to build dynamic, single-page web apps by taking advantage of a virtual DOM to update the elements on a web page quickly and efficiently in a similar way to React. It also uses a single object that’s responsible for keeping track of the application’s state, just like Redux. This makes it easier to manage the state of the app and make sure that different elements don’t get out of sync with each other. The main influence behind Hyperapp was the Elm architecture.
At its core, Hyperapp has three main parts:
  • State. This is a single object tree that stores all of the information about the application.
  • Actions. These are methods that are used to change and update the values in the state object.
  • View. This is a function that returns virtual node objects that compile to HTML code. It can use JSX or a similar templating language and has access to the state and actions objects.
These three parts interact with each other to produce a dynamic application. Actions are triggered by events on the page. The action then updates the state, which then triggers an update to the view. These changes are made to the Virtual DOM, which Hyperapp uses to update the actual DOM on the web page.
Getting Started
To get started as quickly as possible, we’re going to use CodePen to develop our app. You need to make sure that the JavaScript preprocessor is set to Babel and the Hyperapp package is loaded as an external resource using the following link:
https://unpkg.com/hyperapp
To use Hyperapp, we need to import the app function as well as the h method, which Hyperapp uses to create VDOM nodes. Add the following code to the JavaScript pane in CodePen:
const { h, app } = hyperapp;
We’ll be using JSX for the view code. To make sure Hyperapp knows this, we need to add the following comment to the code:
/** @jsx h */
The app() method is used to initialize the application:
const main = app(state, actions, view, document.body);
This takes the state and actions objects as its first two parameters, the view() function as its third parameter, and the last parameter is the HTML element where the application is to be inserted into your markup. By convention, this is usually the <body> tag, represented by document.body.
To make it easy to get started, I’ve created a boilerplate Hyperapp code template on CodePen that contains all the elements mentioned above. It can be forked by clicking on this link.
Hello Hyperapp!
Let’s have a play around with Hyperapp and see how it all works. The view() function accepts the state and actions objects as arguments and returns a Virtual DOM object. We’re going to use JSX, which means we can write code that looks a lot more like HTML. Here’s an example that will return a heading:
const view = (state, actions) => (
  <h1>Hello Hyperapp!</h1>
);
This will actually return the following VDOM object:
{
  name: "h1",
  props: {},
  children: "Hello Hyperapp!"
}
The view() function is called every time the state object changes. Hyperapp will then build a new Virtual DOM tree based on any changes that have occurred. Hyperapp will then take care of updating the actual web page in the most efficient way by comparing the differences in the new Virtual DOM with the old one stored in memory.
Components
Components are pure functions that return virtual nodes. They can be used to create reusable blocks of code that can then be inserted into the view. They can accept parameters in the usual way that any function can, but they don’t have access to the state and actions objects in the same way that the view does.
In the example below, we create a component called Hello() that accepts an object as a parameter. We extract the name value from this object using destructuring, before returning a heading containing this value:
const Hello = ({name}) => <h1>Hello {name}</h1>;
We can now refer to this component in the view as if it were an HTML element entitled <Hello />. We can pass data to this element in the same way that we can pass props to a React component:
const view = (state, actions) => (
  <Hello name="Hyperapp" />
);
Note that, as we’re using JSX, component names must start with capital letters or contain a period.
State
The state is a plain old JavaScript object that contains information about the application. It’s the “single source of truth” for the application and can only be changed using actions.
Let’s create the state object for our application and set a property called name:
const state = {
  name: "Hyperapp"
};
The view function now has access to this property. Update the code to the following:
const view = (state, actions) => (
  <Hello name={state.name} />
);
Since the view can access the state object, we can use its name property as an attribute of the <Hello /> component.
The post Build a To-do List with Hyperapp, the 1KB JS Micro-framework appeared first on SitePoint.