An alternative implementation of React.

For clarity. The code base is tiny compared to React but React's core functionality is nonetheless implemented faithfully, as far as it goes. It led to a greater appreciation of React. There is also Inference to go hand in hand with Reaction, although you may find the useEffects() hook just as useful.

If you like Reaction then you might like Reaction with Style and you should also now look at Reaction Hooks.

With npm:

npm install reaction

You can also clone the repository with Git...

git clone https://github.com/djalbat/reaction.git

...then install the dependencies with npm from within the project's root directory:

npm install

You can also run a development server, see the section on building later on.

There is a small development server that can be run from within the project's directory with the following command:

npm start

The examples will then be available at the following URL:

http://localhost:8888

The source for the examples can be found in the src/examples.js file and corresponding src/example folder. You are encouraged to try the examples whilst reading what follows. You can rebuild them on the fly with the following command:

npm run watch-debug

The development server will reload the page whenever you make changes.

One last thing to bear in mind is that this package is included by way of a relative rather than a package import. If you are importing it into your own application, however, you should use the standard package import.

In order to make use of JSX, you must import the React object at the top of the file in question:

import { React } from "reaction";

...

Now just write your JSX and React code in the normal way.

The ReactDOM class is also available:

import { ReactDOM } from "reaction";

...

You will need to call the ReactDOM.render(...) method at least once from somewhere.

• React components
• React functions
• React classes
• Component state
• References (via the ref property)
• Contexts

Of the component lifecycle methods, only these methods are supported:

• render()
• setInitialState()
• getChildContext()
• componentDidMount()
• componentWillUnmount()

There is one additional lifecycle method:

• childContextSet()

For details see the Raction Hooks readme file.

These methods can be called against any element bar text elements, except for the last two, which can only be called against text elements. The getTagName() method will return null for all but virtual DOM elements, namely those elements with an underlying DOM element.

• on(eventType, handler)
• off(eventType, handler)
• setAttribute(name, value)
• getAttribute(name)
• clearAttribute(name)
• addAttribute(name, value)
• removeAttribute(name)
• hasAttribute(name)
• setClass(className)
• addClass(className)
• removeClass(className)
• toggleClass(className)
• hasClass(className)
• hasClasses(classNames)
• clearClasses()
• getTagName()
• setStyle(name, value)
• getStyle()
• getText()
• setText(text)

There are the following methods to handle state:

• getState()
• setState()
• updateState()

The setState() method will set the React element's state to the given state. The updateState() method will assign the given state to the element's state, which is more akin to React's setState() method. Both will force the component to be remounted.

Mixins are supported for components, whether created by way of extending the Component class or by calling the React.createClass() method. However, Reaction now supports component methods, in line with React, making mixins redundant in the case of extending the Component class. See the subsection immediately below for more details.

When extending the Component class you can assign the mixins to the class...

class ExampleComponent extends Component {
  ...
}

Object.assign(ExampleComponent, {
  mixins: [
    expand,
    collapse
  ]
});

...or, equivalently, use static class fields:

class ExampleComponent extends Component {
  static mixins = [
    expand,
    collapse
  ]
}

When calling the React.createClass() method you should add a mixin property to the plain old JavaScript object that you pass in:

const exampleComponent = React.createClass({
  ...

  mixins: [
    expand,
    collapse
  ]
});

You can safely call mixins from within lifecycle methods and there is nothing wrong with their judicious use.

Reaction now supports component methods, in line with React, making mixins redundant in the case of extending the Component class. For example, instead of...

class ExampleComponent extends Component {
  static mixins = [
    expand,
    collapse
  ]
}

function expand() {
  ...
}

function collapse() {
  ...
}

...the following will do:

class ExampleComponent extends Component {
  expand() {
    ...
  }
    
  collapse() {
    ...
  }
}

Note that mixins will continue to be supported for backwards compatibility. Note also that component methods can be invoked from mixins by way of the this keyword and vice versa.

Contexts are handled slightly differently to React. The default context is an empty plain old JavaScript object {} and this is passed down from parent elements to their children by reference. If you implement any getChildContext() methods, however, it is recommended that you pass down contexts by value. To do so, you can make use of Object.assign() to effectively clone the context passed in, before amending it and passing it on. Suppose you wish to appraise child elements of their parent element, for example. The parent element's component class might look like the following:

class ParentComponent extends Component {
  getChildContext(context) {
    const parentElement = this, ///
          childContext = Object.assign({}, context, {
            parentElement
          });

    return childContext;
  }

  ...
}

And the child element's component class might look like the following:

class ChildComponent extends Component {
  getChildContext(context) {
    const { parentElement } = context,
          childContext = Object.assign({}, context);

    delete childContext.parentElement;

    return childContext;
  }

  ...
}

Passing contexts by value in this way will stop one set of components adversely affecting the contexts of others, so long as unique property names are used.

The functionality of the forceUpdate() method has recently changed. It now simply calls the remount() method and passes on the update it receives as an argument. This impacts updates in the following ways:

• When an element is first mounted, its render() method is called without an update.

• When an element's state is changed, its render() method is again called without an update.

In either case, because the element is being mounted or re-mounted, the render() method should return the element's children. It is perfectly safe to return null or undefined on occasion, however. In either case the return value will be coerced to an empty array.

Guidance on how to handle updates can be found in the 'Recommended patterns' section at the foot of the Inference readme file.

Automation is thanks to npm scripts, have a look at the package.json file. The pertinent commands are:

npm run build-debug
npm run watch-debug

• The SVG tag and attribute names were taken from Titus Wormer's svg-element-attributes package.

• james.smith@djalbat.com