ReactJS - Higher Order Components


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Higher order components are JavaScript functions which are used for adding additional functionality to existing component. These functions are pure which means they are receiving data and returning values according to that data. If data changes, higher order functions is re-run again with different data input. If we want to update our returning component, we don't have to change our HOC. All we need to do is change the data that our function is using.

Higher order component (HOC) is wrapping around "normal" component and provide additional data input. It is actually a function that takes one component and returns another component that wraps the original one.

In this tutorial we will use simple example, so you can easily understand how this concept works. The MyHOC is a higher order function that is used only to pass data to MyComponent. This function takes MyComponent, enhances it with newData and returns the enhanced component that will be rendered on screen.

import React from 'react';

var newData = {
   data: 'Data from HOC...',
}

var MyHOC = ComposedComponent ⇒ class extends React.Component {

   componentDidMount() {
      this.setState({
         data: newData.data
      });
   }

   render() {
      return <ComposedComponent {...this.props} {...this.state} />;
   }
};


class MyComponent extends React.Component {
   render() {
      return (
         <div>
            <h1>{this.props.data}</h1>
         </div>
      )
   }
}

export default MyHOC(MyComponent);

If we run the app, we will see that data is passed to MyComponent.

React HOC Output

NOTE

Higher order components can be used for different functionalities. These pure functions are essence of functional programming. Once you are used to it you will notice how your app is becoming easier to maintain or to upgrade.



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