Why use virtual DOM?

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Virtual DOM (Virtual DOM) is a technology that separates the state of the application from the DOM. It's a JavaScript object whose structure resembles that of an actual DOM element. The purpose of using virtual DOM is to improve the performance and responsiveness of the application while reducing the number of DOM operations.

When the state of the application changes, the virtual DOM can be used to calculate which DOM operations need to be performed to update the UI interface, so that only the necessary parts need to be updated instead of the entire DOM tree. This reduces the number of browser re-renders, which improves performance.

In addition, virtual DOM can also help developers to develop components more conveniently, because each component can have its own virtual DOM. This can make components more independent, easier to maintain and reuse.

In short, virtual DOM is a technology to optimize front-end performance, which can reduce the cost of DOM operations, and can improve development efficiency and code maintainability.

1. How to use virtual DOM to improve application performance?

Batch update: When performing multiple DOM operations, combine them into one batch update operation to reduce the number of DOM operations. For example, in React, multiple states can be updated at once using the setState({}) method.

Avoid unnecessary rendering: Use methods such as shouldComponentUpdate() or React.memo() to avoid unnecessary component rendering. This can reduce the number of comparisons of the virtual DOM, thereby reducing the number of operations of the real DOM.

Use the key attribute: When rendering the list, add a unique key attribute to each list item. In this way, when the list items change, the virtual DOM can find out which list items need to be updated more quickly, thereby improving performance.

Use asynchronous update: When performing some time-consuming operations, you can use asynchronous update to reduce the number of DOM operations. For example, you can use the second parameter of React's setState() method, which is the callback function, to perform asynchronous updates.

Use virtual DOM optimization libraries: Use some optimization libraries, such as React, Vue, etc., which have built-in optimization strategies for virtual DOM, which can help developers reduce the workload of manual optimization.

2. What optimization libraries can help developers further improve the performance of virtual DOM?

React: React, one of the most popular JavaScript libraries out there, uses a virtual DOM to improve performance. React has some optimization strategies built in, such as the shouldComponentUpdate() method and the React.memo() function, which can help developers avoid unnecessary component rendering and thus improve performance.

Vue.js: Vue.js is another popular JavaScript library that also uses virtual DOM to improve performance. Vue.js has some built-in optimization strategies, such as v-if and v-for directives, which can help developers reduce unnecessary DOM operations, thereby improving performance.

Preact: Preact is a lightweight React replacement, its API is similar to React, but it is lighter and faster than React. Preact uses virtual DOM to improve performance. Its size is only about 3KB and can be used in scenarios with high performance requirements.

Inferno: Inferno is another lightweight JavaScript library, its API is similar to React, but it is faster and lighter than React. Inferno uses virtual DOM and some optimization tricks to improve performance and can be used in scenarios with high performance requirements.

3. In addition to virtual DOM, what other technologies can improve front-end performance

Lazy loading: Divide the content of the web page into multiple parts and load it when the user scrolls to a specific part, which can reduce the initial loading time and bandwidth usage.

Image optimization: compressing, reducing size, lazy loading and other operations on images can reduce page loading time.

CDN (Content Distribution Network): CDN can be used to distribute the static resources of the website (such as CSS, JavaScript, pictures, etc.) to servers around the world, thereby speeding up the loading speed of the website.

Caching: Using browser caching or server-side caching can reduce network requests, thereby improving website performance.

Compressed code: Compressing JavaScript and CSS code can reduce file size, thereby reducing loading time.

Use Web Workers: Putting some time-consuming operations into Web Workers can reduce the burden on the main thread, thereby improving the performance and response speed of the page.

Use HTTP/2: Use HTTP/2 to reduce page load time because it supports features such as multiplexing and server push. .