Use of react: How React renders UI

This article introduces to you the use of react: How React renders UI has a certain reference value. Friends in need can refer to it.

01. The way React renders the interface

Before the emergence of large front-end frameworks such as React, the way we rendered UI elements was to use String templates. In React, we render UI elements by using JavaScript objects.

As we mentioned in the previous chapter, React proposed the concept of virtual DOM in order to save the front-end performance consumed by frequent DOM operations. The JavaScript object we create here is Virtual DOM node used to describe "what the page looks like". How is "virtual DOM" finally transformed into "real DOM" and displayed in the browser? The complex work here (manipulating the DOM tree, adding nodes) is done by React.

Let us first look at how to create a virtual DOM node (ie React element) through a JavaScript object:

// 为了创建一个 React 元素，我们需要使用 React.createElement API
const element = React.createElement(
  'h1',
  {className: 'greeting'},
  'Hello, world!'
);

The API will eventually return a JavaScript object in the following format:

const element = {
  type: 'h1',
  props: {
    className: 'greeting',
    children: 'Hello, world'
  }
};

React will find a place for this JavaScript object in the generated virtual DOM tree, and eventually merge it with the real DOM tree in the browser to render the view.

However, in actual development, you will rarely use the React.createElement API, but create React elements as follows:

const element = (
  <h1 className="greeting">
    Hello, world!
  </h1>
);

This creation method is It is implemented through a JavaScript syntax extension called JSX. I will not elaborate further on the concept of JSX here. You can understand it as a kind of simplicity. Syntactic sugar for efficiently creating React elements, used to build the virtual DOM of the entire application more elegantly.

It is worth mentioning that JSX is not part of the React framework (this stems from the philosophy of divide and conquer as much as possible in React code organization), so React is not responsible for merging virtual DOM and real Like the DOM, it is responsible for converting code written in JSX syntax into JavaScript objects using the React.createElement API.

Then who will do this? The answer is Babel. Usually, we use webpack to package our JavaScript code and send it to Babel for translation. Now you understand why React, webpack and Babel always appear together like conjoined twins.

So far, we already know how to create React elements, but in fact we just "Create", before the element is actually displayed on the browser, we also check the key One step "rendering".

Here we speed up. If we want to render the previously created React element, we need to use the following code:

<p id="root"></p>

const element = <h1>Hello, world</h1>;

// 使用 ReactDOM.render API
ReactDOM.render(
  element,
  document.getElementById('root')
);

Yes, the id is root The DOM element will become the root node of the entire virtual DOM tree. So far, we have mastered the entire process of converting React elements into virtual DOM nodes and then rendering the elements on the browser. However, just being able to use React to render visual elements is far from realizing the value of React. Don’t forget that React exists as a large-scale front-end framework (although compared to other large-scale front-end frameworks, its components are not complete). The real value of React is: Use React elements to implement various complex tasks concisely and efficiently Business logic.

How to do this? The answer is to use React components.

02. React components

React components not only give us the ability topackage a bunch of visual elementsbut also give us the ability to packagea series of corresponding Interaction behavior. It can be said: React components are the cornerstone of React applications.

So what is a React component? You can imagine that a React component is like a factory, which receives a series of materials called properties, and ultimately produces (returns) React elements/components.

Let’s put it another way, a React component is essentially a JavaScript function that receives a series of parameters and returns a React element/component. Let's see how it is written:

import React form 'react'
import ReactDOM form 'react-dom'

function Button(props) {
    return <button>{props.buttonName}</button>
}

See, React components fully comply with the componentization idea we mentioned before, receiving parameters and returning UI elements.

It’s a great idea to think about building React applications from a component perspective, because componentization means modularity and reusability. Component classes are like instances of a factory producing components. These component classes fully comply with the "Single Response Principle" and "DOT" principles.

In React’s official documentation, a large number of React APIs are about components. Therefore, components are a very important concept in React. In essence, components are the main encapsulation unit given to us by React. Through components, we can quickly build a large application with complex interaction logic and visual interface like building blocks, and each visual unit in the application has very clear responsibilities.

Hopefully by this point you can appreciate the value of React when building large applications. It allows us to focus on a small part of the application without inadvertently affecting the rest of the application (i.e. each component In line with the principle of "high cohesion, low coupling"). Using React, it is easier for us to write clear and elegant code.

03. Summary

Finally, let us once again summarize the two advantages of using components to render interfaces in React:

1. Easy to reuse : We can call a component at any time and place;

2. Convenient customization: By giving different attributes to the component, we can get different UI elements;

Related recommendations:

Use of React: Five major features of the react framework

Introduction to responsive React Native Echarts components

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