What is Element
What is Element in React.js and React Native?
In the context of React.js and React Native, an element is a fundamental building block that defines what you see on the screen. Unlike traditional HTML elements, React elements are plain objects that describe what you want to appear in the UI. They are immutable, meaning once created, they cannot be changed. This immutability is crucial for the efficient updating and rendering of the UI, as it allows React to quickly determine what has changed and update only those parts of the DOM.
Creating React Elements
React elements can be created using the `React.createElement` function or JSX syntax. The `React.createElement` function takes three arguments: the type of the element, a configuration object (props), and the children of the element. For example, `React.createElement(‘div’, { className: ‘container’ }, ‘Hello World’)` creates a `div` element with a class of ‘container’ and text content ‘Hello World’. JSX, on the other hand, provides a more concise and readable way to create elements, allowing you to write `
`.
React Elements vs Components
It’s important to distinguish between React elements and React components. While elements are the smallest building blocks of React applications, components are larger, reusable pieces of the UI. Components can be either functional or class-based and can return React elements as their output. When a component is rendered, it returns a tree of React elements, which React then uses to update the DOM.
Rendering Elements
Rendering a React element into the DOM is done using the `ReactDOM.render` method in React.js or the `AppRegistry.registerComponent` method in React Native. These methods take a React element and a DOM container or a root component, respectively. For example, `ReactDOM.render(, document.getElementById(‘root’))` renders the `App` component into the DOM element with the id ‘root’. This process is what makes the UI interactive and dynamic.
Updating Elements
React elements are immutable, so to update the UI, you need to create a new element and render it again. React’s reconciliation algorithm efficiently updates the DOM by comparing the new element with the previous one and making the minimal necessary changes. This process is known as “diffing” and is a core part of React’s performance optimizations.
Props and State
React elements can receive data through props, which are read-only attributes passed from parent components. Props allow you to customize elements and components, making them more flexible and reusable. State, on the other hand, is a way to manage dynamic data within a component. While props are immutable, state can change over time, triggering re-renders and updates to the UI.
Children in React Elements
React elements can have children, which are other React elements nested inside them. This nesting allows you to build complex UIs from simple, reusable components. The `children` prop is a special prop that can be used to pass elements or components as children. For example, “ renders the `Child` component inside the `Parent` component.
Fragment Elements
React provides a special type of element called a Fragment, which allows you to group multiple elements without adding extra nodes to the DOM. Fragments are useful when you need to return multiple elements from a component without wrapping them in a parent element. You can create a Fragment using the `React.Fragment` component or the shorthand syntax `…`.
Key Attribute
When rendering lists of elements, React requires a special `key` attribute to identify each element uniquely. The `key` attribute helps React optimize the rendering process by keeping track of which items have changed, been added, or removed. Keys should be unique and stable, typically using an identifier from your data.
Portals
React Portals provide a way to render elements outside the main DOM hierarchy of the parent component. This is useful for scenarios like modals, tooltips, or any UI element that needs to visually break out of its container. You can create a portal using the `ReactDOM.createPortal` method, which takes a React element and a DOM node as arguments.