React, part 2

HOC

Higher-Order Components

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

const EnhancedComponent = higherOrderComponent(WrappedComponent);

Details

Simple HOC

    // Take in a component as argument WrappedComponent
    function simpleHOC(WrappedComponent) {
      // And return a new anonymous component
      return class extends React.Component{
        render() {
          return <WrappedComponent {...this.props}/>;
        }
      }
    }

// Create a new component
const NewComponent = simpleHOC(Hello);

// Using
<NewComponent/>

Fragments

A common pattern in React is for a component to return multiple elements. Fragments let you group a list of children without adding extra nodes to the DOM.

render() {
  return (
    <React.Fragment>
      <ChildA />
      <ChildB />
      <ChildC />
    </React.Fragment>
  );
}

Details

Usage

class Columns extends React.Component {
  render() {
    return (
      <React.Fragment>
        <td>Hello</td>
        <td>World</td>
      </React.Fragment>
    );
  }
}

class Columns extends React.Component {
  render() {
    return (
      <>
        <td>Hello</td>
        <td>World</td>
      </>
    );
  }
}

Stateful vs. Stateless

A stateless component is usually associated with how a concept is presented to the user. It is similar to a function in that, it takes an input (props) and returns the output (react element).

A stateful component is always a class component. It is created by extending the React.Component class. A stateful component is dependent on it’s state object and can change it’s own state. The component re-renders based on changes to it’s state, and may pass down properties of it’s state to child components as properties on a props object.

PropTypes

Usage

npm install --save prop-types

import PropTypes from 'prop-types';

class Greeting extends React.Component {
  render() {
    return (
      <h1>Hello, {this.props.name}</h1>
    );
  }
}

Greeting.propTypes = {
  name: PropTypes.string
};

Greeting.defaultProps = {
  name: 'Stranger'
};

Syntax, base type

import PropTypes from 'prop-types';

MyComponent.propTypes = {
  // You can declare that a prop is a specific JS type. By default, these
  // are all optional.
  optionalArray: PropTypes.array,
  optionalBool: PropTypes.bool,
  optionalFunc: PropTypes.func,
  optionalNumber: PropTypes.number,
  optionalObject: PropTypes.object,
  optionalString: PropTypes.string,
  optionalSymbol: PropTypes.symbol,
};

Syntax, react elements

import PropTypes from 'prop-types';

MyComponent.propTypes = {
  // Anything that can be rendered: numbers, strings, elements or an array
  // (or fragment) containing these types.
  optionalNode: PropTypes.node,

  // A React element.
  optionalElement: PropTypes.element,

  // A React element type (ie. MyComponent).
  optionalElementType: PropTypes.elementType,
};

Syntax, arrays and objects

import PropTypes from 'prop-types';

MyComponent.propTypes = {
  // You can also declare that a prop is an instance of a class. This uses
  // JS's instanceof operator.
  optionalMessage: PropTypes.instanceOf(Message),

  // An array of a certain type
  optionalArrayOf: PropTypes.arrayOf(PropTypes.number),

  // An object with property values of a certain type
  optionalObjectOf: PropTypes.objectOf(PropTypes.number),

  // An object taking on a particular shape
  optionalObjectWithShape: PropTypes.shape({
    color: PropTypes.string,
    fontSize: PropTypes.number
  }),
  
  // An object with warnings on extra properties
  optionalObjectWithStrictShape: PropTypes.exact({
    name: PropTypes.string,
    quantity: PropTypes.number
  }),   
};

Syntax, type combination

import PropTypes from 'prop-types';

MyComponent.propTypes = {
  // You can ensure that your prop is limited to specific values by treating
  // it as an enum.
  optionalEnum: PropTypes.oneOf(['News', 'Photos']),

  // An object that could be one of many types
  optionalUnion: PropTypes.oneOfType([
    PropTypes.string,
    PropTypes.number,
    PropTypes.instanceOf(Message)
  ]),
};

Syntax, isRequired and any

import PropTypes from 'prop-types';

MyComponent.propTypes = {
  // You can chain any of the above with `isRequired` to make sure a warning
  // is shown if the prop isn't provided.
  requiredFunc: PropTypes.func.isRequired,

  // A value of any data type
  requiredAny: PropTypes.any.isRequired,
};