#React

Material UI uses Emotion as its default styling engine.

Run the following commands to add Material UI to your project:

npm install @mui/material @emotion/react @emotion/styled

Emotion Emotion is a library designed for writing css styles with JavaScript. It provides powerful and predictable style composition in addition to a great developer experience with features such as source maps, labels, and testing utilities. Both string and object styles are supported.

There are two primary methods of using Emotion. The first is framework agnostic and the second is for use with React.

Styled Components

styled is a way to create React components that have styles attached to them. It’s available from @emotion/styled. styled was heavily inspired by styled-components and glamorous.

import styled from '@emotion/styled'

const Button = styled.button`
  padding: 32px;
  background-color: hotpink;
  font-size: 24px;
  border-radius: 4px;
  color: black;
  font-weight: bold;
  &:hover {
    color: white;
  }
`

render(<Button>This my button component.</Button>)

References

Emotion website

When a component’s props or state change, React decides whether an actual DOM update is necessary by comparing the same with Virtual DOM. If it is not equal React will update the DOM.

React maintains two Virtual DOM at each time, one contains the updated Virtual DOM and one which is just the pre-update version of this updated Virtual DOM. Now it compares the pre-update version with the updated Virtual DOM and figures out what exactly has changed in the DOM like which components have been changed. This process of comparing the current Virtual DOM tree with the previous one is known as ‘diffing’.

The algorithm used for diffing is known as Diffing Algorithm.

Once React finds out what exactly has changed then it updated those objects only, on real DOM. React uses something called batch updates to update the real DOM. It just means that the changes to the real DOM are sent in batches instead of sending any update for a single change in the state of a component. This entire process of transforming changes to the real DOM is called Reconciliation

References

geeksforgeeks

A common pattern is for a component to return a list of children. In the below example when Column component is rendering the HTML will be invalid as a div is coming in the middle of the table. Whenever we are using Fragments, we can avoid that.

Take this example React snippet:

class Table extends React.Component {
  render() {
    return (
      <table>
        <tr>
          <Columns />
        </tr>
      </table>
    );
  }
}

would need to return multiple elements in order for the rendered HTML to be valid. If a parent div was used inside the render() of , then the resulting HTML will be invalid.

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

results in a output of:

<table>
  <tr>
    <div>
      <td>Hello</td>
      <td>World</td>
    </div>
  </tr>
</table>

Fragments declared with the explicit <React.Fragment> syntax may have keys. A use case for this is mapping a collection to an array of fragments — for example, to create a description list:

function Glossary(props) {
  return (
    <dl>
      {props.items.map(item => (
        // Without the `key`, React will fire a key warning
        <React.Fragment key={item.id}>
          <dt>{item.term}</dt>
          <dd>{item.description}</dd>
        </React.Fragment>
      ))}
    </dl>
  );
}

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>
  );
}

Short Syntax

Here is the shorter syntax you can use for declaring fragments. It looks like empty tags:

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

Motivation for fragments in React.