What is DOM ?
React DOM (short for Document Object Model) is the package in the React library that is responsible for rendering React components to the DOM. DOM Elements
It provides a way to take a React component and attach it to an existing DOM element.
The React DOM package exports a number of methods that you can use to manipulate the DOM, such as ReactDOM.render() which is used to render a React component to the DOM and ReactDOM.unmountComponentAtNode() which is used to unmount a React component from the DOM.
You can use React DOM to declaratively update the DOM with your components, rather than manually manipulating the DOM with imperative code. This can help make your code easier to understand and maintain, as well as improve performance by minimizing the number of DOM manipulations that need to occur.
React provides a way to create DOM elements using a syntax that is similar to HTML. For example, you can create a div element like this:
const element = <div>Hello, world!</div>
You can also pass props (short for properties) to a DOM element to specify additional attributes or data for the element. For example:
const element = <div className="greeting">Hello world!</div>;
This creates a div element with a class of greeting and a content of “Hello, world!”.
You can also nest elements inside other elements to create more complex structures. For example:
const element = (
<div className="container">
<h1>Hello world!</h1>
<p>This is a simple React component.</p>
</div>
);
This creates a div element with a class of container, containing an h1 element and a p element.
You can then use these elements to render content to the DOM using the ReactDOM.render() method. For example:
ReactDOM.render(element, document.getElementById('root'));
This will render the element tree to the DOM, starting at the element with an ID of root.
React uses a virtual DOM (VDOM) to update the real DOM efficiently. The virtual DOM is a lightweight in-memory representation of the actual DOM.
When a component’s state changes, React updates the virtual DOM to reflect the new state. It then compares the virtual DOM to the previous version of the virtual DOM and calculates the minimal set of changes that need to be made to the real DOM in order to reflect the new state. Finally, React updates the real DOM with these minimal changes.
Using the virtual DOM to update the real DOM in this way can significantly improve performance, particularly in large applications with many components that may need to be re-rendered when their state changes. It helps to avoid expensive DOM manipulation operations, such as recalculating styles or layouts, which can be slow and cause the UI to become unresponsive.
Instead of directly manipulating the real DOM, you write code that describes how the UI should look using React components. React then uses the virtual DOM to efficiently update the real DOM to match your desired UI. This can help make your code easier to understand and maintain, as well as improve performance.
Difference between Virtual and Real Dom ?
The main difference between the virtual DOM and the Real DOM is that the virtual DOM is an in-memory representation of the actual DOM, while the real DOM is the actual DOM itself.
The virtual DOM is a lightweight copy of the real DOM that is used to optimize updates to the real DOM. When a component’s state changes, React updates the virtual DOM to reflect the new state. It then calculates the minimal set of changes that need to be made to the real DOM in order to reflect the new state, and updates the real DOM with these minimal changes.
This process of updating the virtual DOM and then updating the real DOM with the minimal set of changes helps to improve performance, particularly in large applications with many components that may need to be re-rendered when their state changes. It avoids expensive DOM manipulation operations, such as recalculating styles or layouts, which can be slow and cause the UI to become unresponsive.
The real DOM, on the other hand, is the actual DOM that is rendered in the browser. It is the actual tree of DOM nodes that represents the structure of the UI. When you update the real DOM, the changes are immediately reflected in the UI.
In summary, the virtual DOM is a way to optimize updates to the real DOM in React, while the real DOM is the actual DOM that is rendered in the browser.
Here is a simple example of how the virtual DOM is used in React to update the real DOM:
import React from 'react';
import ReactDOM from 'react-dom';
class MyComponent extends React.Component {
state = {
count: 0
};
handleClick = () => {
this.setState({
count: this.state.count + 1
});
}
render() {
return (
<div>
<button onClick={this.handleClick}>Click me</button>
<p>You have clicked the button {this.state.count} times.</p>
</div>
);
}
}
ReactDOM.render(<MyComponent />, document.getElementById('root'));
In this example, the MyComponent class is a React component that displays a button and a paragraph. The button has an onClick event handler that increments a count state variable when clicked. The paragraph displays the current value of the count state variable.
When the component is first rendered, the virtual DOM is created and used to update the real DOM with the initial UI. When the button is clicked, the component’s state changes, and the virtual DOM is updated to reflect the new state. React then compares the new virtual DOM to the previous version of the virtual DOM and calculates the minimal set of changes that need to be made to the real DOM. Finally, React updates the real DOM with these minimal changes, causing the UI to be updated to reflect the new state.
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