In this section we will try to understand raw React API, how we implement them ,what do they do and how are they different from just generating DOM Nodes with Vanilla JavaScript.
In the previous section we saw how to create DOM elements, how we append them to the DOM tree so we can see our element.
...
<body>
<div id="root"></div>
<script type="module">
const rootElement = document.getElementById('root')
// We always need to append the root element to the document
document.body.append(rootElement);
</script>
</body>
...
React abstracts away the imperative browser API from you to give you a much more declarative API to work with.
Learn more about the difference between those two concepts here: Imperative vs Declarative Programming
With that in mind, you need two JavaScript files to write React applications for the web:
- React: responsible for creating React elements (kinda like
document.createElement()) - ReactDOM: responsible for rendering React elements to the DOM (kinda like
rootElement.append())
Let's convert our file to use React! using just raw React APIs here.
In modern applications you'll get React and React DOM files from a "package registry" like npm (react and react-dom).
But we will use https://unpkg.com/. It's CDN (global content delivery network) that will allow us ready-to-use script files in regular script tags so you don't have to bother installing them.
...
<body>
<div id="root"></div>
<script src="https://unpkg.com/react@17.0.0/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@17.0.0/umd/react-dom.development.js"></script>
<script type="module">
const rootElement = document.getElementById('root')
// We always need to append the root element to the document
document.body.append(rootElement);
</script>
</body>
...
That's it. We have React and ReactDOM as global variable that we can use in our code
React.createElement()
Syntax:
React Top-Level API – React
legacy.reactjs.org
React.createElement() takes three arguments. They are:
-
type: The type argument can be either a HTML element tag name string (such as
'div'or'span'), a React component type (a class or a function), or a React fragment type. - props: n object containing properties ('props' in React terms) that get passed to the component. Since we're just getting started with React, we won't use these just yet — but be aware that the second options serves this purpose.
- children: the last argument is the children of that component. This can be a quoted string in which case the content will be interpreted as text. However, we can also pass in a reference to another component, allowing us to nest elements and components within each other
The third and subsqeuent arguments to
React.createElement()are always added to thepropsaschildren— regardless of the type.
So if you create an element with a custom type and children, you can access those children on its props.
In fact, these two createElement() calls are equivalent:
If we want one child for our element we can provide it within the props like the example below
// Children as prop
const element = React.createElement('div', {
className: 'container',
children: 'Hello World',
})
// children as createElement THird argument
const element = React.createElement('div', {className: 'container'},'Hello World',)
But if we want to add multiple children, then we can only use the third argument
const title = React.createElement('h1', {}, 'My First React Code');
const paragraph = React.createElement('p', {}, 'Writing some more HTML. Cool stuff!');
const container = React.createElement('div', {}, [title, paragraph]);
Children's children
We can nest children as much as we want. We also don't need to store our elements in variables before using them, we can declare them inline as well (though the downside of this is less readable code):
import React from 'react';
import ReactDOM from 'react-dom';
const list =
React.createElement('div', {},
React.createElement('h1', {}, 'My favorite fruit'),
React.createElement('ul', {},
[
React.createElement('li', {}, 'orange'),
React.createElement('li', {}, 'apple'),
React.createElement('li', {}, 'Banana')
]
)
);
ReactDOM.render()
One important thing to know about React is that it supports multiple platforms (for example, native, web, VR). Each of these platforms has its own code necessary for interacting with that platform, and then there's shared code between the platforms.
Syntax:
ReactDOM – React
legacy.reactjs.org
ReactDOM.render() takes two arguments:
- element: The element that needs to be rendered in the DOM.
- containerElement: Where to render in the DOM.
React implements a browser-independent DOM system for performance and cross-browser compatibility and renders it using ReactDOM().
The React Element objects that
React.createElement()returns are just plain old JavaScript objects that describe the DOM nodes that you’d likeReactDOM.render()to create. They’re **_not*_* DOM nodes, and _not*_* added to the document. They’re just objects.**
ReactDOM()will create a DOM node and append or render our react app into a specific element that's going to behave as our app root
Let's see how our code will be using these two script files
...
<body>
<div id="root"></div>
<script src="https://unpkg.com/react@17.0.0/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@17.0.0/umd/react-dom.development.js"></script>
<script type="module">
const element = React.createElement('div', {
className: 'container',
children: 'Hello World',
})
ReactDOM.render(element, document.getElementById('root'));
</script>
</body>
...
References and articles:
Top-Level API | React
zhenyong.github.io
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