React Components

Designing Components

Resources

These can found here https://github.com/pkellner/pluralsight-designing-react-components-course-code Implements

• Component Reuse
• Single Responsibility
• Dont Repeat Yourself

Next JS Setup

Create project with

npm install react react-dom next --save

Add three commands to packages.json

"dev": "next",
"build": "next build",
"start": "next start"

Basic Page

In the demo the tutor builds an app which looks like this
With next js we can create a basic page using images to represent components

function Page() {
    return (
        <div>
            <img src="images/header.png" />
            <img src="images/menu.gif" />
            <img src="images/searchbar.gif" />
            <img src="images/speakers.png" />
            <img src="images/footer.png" />
        </div>
    )
}
export default Page

Replacing with Components

To start making our components we can replace the images with components. For example

import React from 'react'
const Header = () => <img src="images/header.png" />
export default Header

And replace the Page with the components i.e.

function Page() {
    return (
        <div>
            <Header />
            <Menu />
            <SpeakerSearchBar />
            <Speakers />
            <Footer />
        </div>
    )
}
export default Page

Breaking Down Futher

We can now break down further the speaker image into individual speakers.

const Speakers = () => {
  const speakers = [
    { image: "images/speaker-component-1124.png", name: "a" },
    { image: "images/speaker-component-1530.png", name: "b" },
    { image: "images/speaker-component-10803.png", name: "c" },
  ];
  return (
    <div>
      {speakers.map((x) => {
        return <img src={x.image} alt={x.name} key={x.image} />;
      })}
    </div>
  );
};

export default Speakers;

Component Abstractions

In programming three patterns used to abstract

• HOC - Higher Order Component

A higher-order component is a function that takes a component and returns a new component

• RP - Render Prop

A RP is simply a prop that takes a function which returns elements that will be used in render(). You can pass an element directly into a prop and use it in render() which would make the whole thing a RP by name, but generally, when people speak about RPs, they mean the first definition.

• Context

Context in React is used to share data that is global to a component tree such as an authenticated user or preferred theme without passing that data as props.

HOC

Simple Example of HOC

As specified above a HOS is a function that takes a component and returns a new component

const EnhancedSpeakerComponent = withData(Speakers)
function withData(Component) {
   return function() {
      return <Component />
   }
}
export default EnhancedSpeakerComponent

Move the Data to HOC

Now lets move our array into the HOC to have

const EnhancedSpeakerComponent = withData(Speakers)
function withData(Component) {
    const speakers = [
        { image: "images/speaker-component-1124.png", name: "a" },
        { image: "images/speaker-component-1530.png", name: "b" },
        { image: "images/speaker-component-10803.png", name: "c" },
      ]
   return function() {
      return <Component speakers={speakers} />
   }
}
export default EnhancedSpeakerComponent

And change the component to have speakers as a prop

const Speakers = ({speakers}) => {
  return (
    <div>
      {speakers.map((x) => {
        return <img src={x.image} alt={x.name} key={x.image} />;
      })}
    </div>
  );
};

We can now put the withData in a separate function and import into the Speakers component so we now have.

import React from 'react'
import withData from './withData'

const Speakers = ({speakers}) => {
  return (
    <div>
      {speakers.map((x) => {
        return <img src={x.image} alt={x.name} key={x.image} />;
      })}
    </div>
  );
};
export default withData(Speakers)

Adding Parameter to Our HOC

Lets say we want to limit the number of images. We can do this but passing a value to the function like below

const maxSpeakersToShow = 2
export default withData(maxSpeakersToShow)(Speakers)

This is very similar to how we implement decorators in python, java or other languages because to implement this in the function we simply wrap the function and return it

function withData(maxSpeakersToShow) {
   return function(Component) {
...
   }
}

Here is the full example.

import React from "react";

function withData(maxSpeakersToShow) {
  return function(Component) {
    const speakers = [
      { image: "images/speaker-component-1124.png", name: "a" },
      { image: "images/speaker-component-1530.png", name: "b" },
      { image: "images/speaker-component-10803.png", name: "c" },
    ];

    return function () {
      const limitSpeakers = speakers.slice(0, maxSpeakersToShow)
      return <Component speakers={limitSpeakers} />;
    };
  }
}
export default withData;

Let use the more modern format with lambdas.

const withData = (maxSpeakersToShow) => (Component) => {
  const speakers = [
    { image: "images/speaker-component-1124.png", name: "a" },
    { image: "images/speaker-component-1530.png", name: "b" },
    { image: "images/speaker-component-10803.png", name: "c" },
  ]

  return () => {
    const limitSpeakers = speakers.slice(0, maxSpeakersToShow);
    return <Component speakers={limitSpeakers} />;
  }
}