# React.createClass vs extends React.Component

# Create React Component

Let's explore the syntax differences by comparing two code examples.

# React.createClass (deprecated)

Here we have a const with a React class assigned, with the render function following on to complete a typical base component definition.

import React from 'react';

const MyComponent = React.createClass({
  render() {
    return (
      <div></div>
    );
  }
});

export default MyComponent;

# React.Component

Let's take the above React.createClass definition and convert it to use an ES6 class.

import React from 'react';

class MyComponent extends React.Component {
  render() {
    return (
      <div></div>
    );
  }
}

export default MyComponent;

In this example we're now using ES6 classes. For the React changes, we now create a class called MyComponent and extend from React.Component instead of accessing React.createClass directly. This way, we use less React boilerplate and more JavaScript.

PS: Typically this would be used with something like Babel to compile the ES6 to ES5 to work in other browsers.

# "this" Context

Using React.createClass will automatically bind this context (values) correctly, but that is not the case when using ES6 classes.

# React.createClass

Note the onClick declaration with the this.handleClick method bound. When this method gets called React will apply the right execution context to the handleClick.

import React from 'react';

const MyComponent = React.createClass({
  handleClick() {
    console.log(this); // the React Component instance
  },
  render() {
    return (
      <div onClick={this.handleClick}></div>
    );
  }
});

export default MyComponent;

# React.Component

With ES6 classes this is null by default, properties of the class do not automatically bind to the React class (component) instance.

import React from 'react';

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
  }
  handleClick() {
    console.log(this); // null
  }
  render() {
    return (
      <div onClick={this.handleClick}></div>
    );
  }
}

export default MyComponent;

There are a few ways we could bind the right this context.

# Case 1: Bind inline:

import React from 'react';

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
  }
  handleClick() {
    console.log(this); // the React Component instance
  }
  render() {
    return (
      <div onClick={this.handleClick.bind(this)}></div>
    );
  }
}

export default MyComponent;

# Case 2: Bind in the class constructor

Another approach is changing the context of this.handleClick inside the constructor. This way we avoid inline repetition. Considered by many as a better approach that avoids touching JSX at all:

import React from 'react';

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.handleClick = this.handleClick.bind(this);
  }
  handleClick() {
    console.log(this); // the React Component instance
  }
  render() {
    return (
      <div onClick={this.handleClick}></div>
    );
  }
}

export default MyComponent;

# Case 3: Use ES6 anonymous function

You can also use ES6 anonymous function without having to bind explicitly:

import React from 'react';

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
  }
  handleClick = () => {
    console.log(this); // the React Component instance
  }
  render() {
    return (
      <div onClick={this.handleClick}></div>
    );
  }
}

export default MyComponent;

# Declare Default Props and PropTypes

There are important changes in how we use and declare default props and their types.

# React.createClass

In this version, the propTypes property is an Object in which we can declare the type for each prop. The getDefaultProps property is a function that returns an Object to create the initial props.

import React from 'react';

const MyComponent = React.createClass({
  propTypes: {
    name: React.PropTypes.string,
    position: React.PropTypes.number
  },
  getDefaultProps() {
    return {
      name: 'Home',
      position: 1
    };
  },
  render() {
    return (
      <div></div>
    );
  }
});

export default MyComponent;

# React.Component

This version uses propTypes as a property on the actual MyComponent class instead of a property as part of the createClass definition Object.

The getDefaultProps has now changed to just an Object property on the class called defaultProps, as it's no longer a "get" function, it's just an Object. It avoids more React boilerplate, this is just plain JavaScript.

import React from 'react';

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
  }
  render() {
    return (
      <div></div>
    );
  }
}
MyComponent.propTypes = {
  name: React.PropTypes.string,
  position: React.PropTypes.number
};
MyComponent.defaultProps = {
  name: 'Home',
  position: 1
};

export default MyComponent;

Additionally, there is another syntax for propTypes and defaultProps. This is a shortcut if your build has ES7 property initializers turned on:

import React from 'react';

class MyComponent extends React.Component {
  static propTypes = {
    name: React.PropTypes.string,
    position: React.PropTypes.number
  };
  static defaultProps = {
    name: 'Home',
    position: 1
  };
  constructor(props) {
    super(props);
  }
  render() {
    return (
      <div></div>
    );
  }
}

export default MyComponent;

# Mixins

We can use mixins only with the React.createClass way.

# React.createClass

In this version we can add mixins to components using the mixins property which takes an Array of available mixins. These then extend the component class.

import React from 'react';

var MyMixin = {
  doSomething() {

  }
};
const MyComponent = React.createClass({
  mixins: [MyMixin],
  handleClick() {
    this.doSomething(); // invoke mixin's method
  },
  render() {
    return (
      <button onClick={this.handleClick}>Do Something</button>
    );
  }
});

export default MyComponent;

# React.Component

React mixins are not supported when using React components written in ES6. Moreover, they will not have support for ES6 classes in React. The reason is that they are considered harmful (opens new window).

# Set Initial State

There are changes in how we are setting the initial states.

# React.createClass

We have a getInitialState function, which simply returns an Object of initial states.

import React from 'react';

const MyComponent = React.createClass({
  getInitialState () {
    return {
      activePage: 1
    };
  },
  render() {
    return (
      <div></div>
    );
  }
});

export default MyComponent;

# React.Component

In this version we declare all state as a simple initialisation property in the constructor, instead of using the getInitialState function. It feels less "React API" driven since this is just plain JavaScript.

import React from 'react';

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      activePage: 1
    };
  }
  render() {
    return (
      <div></div>
    );
  }
}

export default MyComponent;

# ES6/React “this” keyword with ajax to get data from server

import React from 'react';

class SearchEs6 extends React.Component{
    constructor(props) {
        super(props);
        this.state = {
            searchResults: []
        };
    }

    showResults(response){
        this.setState({
            searchResults: response.results
        })
    }

    search(url){
        $.ajax({
            type: "GET",
            dataType: 'jsonp',
            url: url,
            success: (data) => {
                this.showResults(data);
            },
            error: (xhr, status, err) => {
                console.error(url, status, err.toString());
            }
        });
    }

    render() {
        return (
            <div>
                <SearchBox search={this.search.bind(this)} />
                <Results searchResults={this.state.searchResults} />
            </div>
        );
    }
}

# Syntax

Case 1: React.createClass({ })
Case 2: class MyComponent extends React.Component { }

# Remarks

React.createClass was deprecated in v15.5 (opens new window) and expected to be removed in v16 (opens new window). There is a drop-in replacement package (opens new window) for those that still require it. Examples using it should be updated.

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