React and ES6 inheritance

By : JBE
Source: Stackoverflow.com
Question!

I have an ES6 class :

class BaseClass {
  getInitialState(){
      return {message: 'Hello!'};
  }

  render() {
      return (
            <div>
                <div>{this.state.message}</div>
            </div>
        )
  }
}

That I can export in ES6 using this expression (source : react ES6 browserify)

export default React.createClass(BaseClass.prototype)

This works fine. Now I would like to use ES6 inheritance to extend my BaseClass class :

class ExtendedClass extends BaseClass{
    getInitialState(){
        return {message: "Hello! I'm an extension"};
    }
}

But when I call React.createClass on the ExtendedClass class, I got the following exception :

Invariant Violation: ReactCompositeComponentInterface: You are attempting to define `constructor` on your component more than once. This conflict may be due to a mixin.

I know React 0.13 is supposed to be more ES6 friendly but is there any ways to handle that ?

EDIT:

I'm using Traceur to compile my ES6 classes. The output for ExtendedClass looks like :

function ExtendedClass() {
  "use strict";
  if (BaseClass !== null) {
    BaseClass.apply(this, arguments);
  }
}
for (BaseClass____Key in BaseClass) {
    if (BaseClass.hasOwnProperty(BaseClass____Key)) {
      ExtendedClass[BaseClass____Key] = BaseClass[BaseClass____Key];
    }
  }
  ____SuperProtoOfBaseClass = BaseClass === null ? null : BaseClass.prototype;
  ExtendedClass.prototype = Object.create(____SuperProtoOfBaseClass);
  ExtendedClass.prototype.constructor = ExtendedClass;
  ExtendedClass.__superConstructor__ = BaseClass;
  ExtendedClass.prototype.getInitialState = function() {
    "use strict";
    return {message: "Hello! I'm an extension"};
  };
  React.createClass(ExtendedClass.prototype);
By : JBE


Answers
There is a great post about writing ReactJS in ES6.

http://ilikekillnerds.com/2015/02/developing-react-js-components-using-es6/

Anyway when using ES6 you don't use React.createClass. you just create class that extends React.Component

Also in ES6 you don't have getInitialState not defaultProps. it's replaced in favor using this.state inside constructor.

Check out this example. Let's say you have Card component and Welcome Panel that extends Card component.

The code is as following:

Card Component:

import React , { Component } from 'react'
class Card extends Component {
  constructor(props){
    super(props);
  }

  render() {
    return (
      <div className="card">
           <div className="card__content">
             <label>{this.props.content}</label>
           </div>
      </div>
      )
  }

  initPanel(el,content){
    React.render( <Card content={content} />, el);   
  }
}

export default Card;

Welcome Panel Component:

import React from 'react';
import Card from 'components/card.component';

class WelcomePanel extends Card {
  constructor(props){
    super(props);
    this.state = {
      content: "Welcome Panel",
      index: 0
    }
  }

  componentClicked(){
    this.setState({content: "Component Clicked", index: this.state.index + 1})
  }

  render() {
    return (
      <div className="welcome-panel" onClick={this.componentClicked.bind(this)}>
         <Card content={`${this.state.content} ${this.state.index > 0 ? this.state.index  : ''} ${this.state.index > 0 ? 'times' : ''} `} />
      </div>
      )
  }

  initPanel(el,content){
    React.render( <WelcomePanel />, el);   
  }
}

export default { Class: WelcomePanel }


Here is the workaround I've found :

Inside React.js library, I've updated the ReactCompositeComponentInterface to add a custom policy for constructor (As far as I know there's no way to customize this 'interface' properly) :

var ReactCompositeComponentInterface = {

/**
 * An array of Mixin objects to include when defining your component.
 *
 * @type {array}
 * @optional
 */
mixins: SpecPolicy.DEFINE_MANY,

/**
 * Custom policy for 'constructor'
 */
constructor: SpecPolicy.DEFINE_MANY,

  ...

}

Then in the ExtendedClass, you have to redefine every method even if you don't customize them :

class ExtendedClass extends BaseClass{
    getInitialState(){
        return {message: "Hello! I'm an extension"};
    }
    /** required */
    render(){
        return super.render();
    }
}

I'm not happy with this dirty solution but it will do the job waiting for a 0.13 version that hopefully will solve those issues.

By : JBE


This video can help you solving your question :)
By: admin