JSX
Learn to use JSX, the basic syntax of React.js
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Key Concepts
Review core concepts you need to learn to master this subject
Nested JSX elements
JSX Syntax and JavaScript
Multiline JSX Expression
JSX syntax and HTML
JSX attributes
ReactDOM JavaScript library
Embedding JavaScript in JSX
The Virtual Dom
Nested JSX elements
Nested JSX elements
const myClasses = (
<a href="https://www.codecademy.com">
<h1>
Sign Up!
</h1>
</a>
);In order for the code to compile, a JSX expression must have exactly one outermost element. In the below block of code the <a> tag is the outermost element.
Intro to JSX
Lesson 1 of 2
- 1React.js is a JavaScript library. It was developed by engineers at Facebook. Here are just a few of the reasons why people choose to program with React: - React is fast. Apps made in React …
- 2Take a look at the following line of code: const h1 = Hello world ; What kind of weird hybrid code is that? Is it JavaScript? HTML? Or something else? It seems like it must be JavaScript,…
- 3Good! Take another look at the line of code that you wrote. Does this code belong in a JavaScript file, an HTML file, or somewhere else? The answer is…a JavaScript file! Despite what it looks…
- 4JSX is a syntax extension for JavaScript. It was written to be used with React. JSX code looks a lot like HTML. What does “syntax extension” mean? In this case, it means that JSX is not valid…
- 5A basic unit of JSX is called a JSX element. Here’s an example of a JSX element: Hello world This JSX element looks exactly like HTML! The only noticeable difference is that you would find i…
- 6JSX elements are treated as JavaScript expressions. They can go anywhere that JavaScript expressions can go. That means that a JSX element can be saved in a variable, passed to a function, sto…
- 7JSX elements can have attributes, just like HTML elements can. A JSX attribute is written using HTML-like syntax: a name, followed by an equals sign, followed by a value. The value shoul…
- 8You can nest JSX elements inside of other JSX elements, just like in HTML. Here’s an example of a JSX element, nested inside of a JSX element: Click me! To make this more readable, …
- 9There’s a rule that we haven’t mentioned: a JSX expression must have exactly one outermost element. In other words, this code will work: const paragraphs = ( I am a paragraph. I,…
- 10You’ve learned how to write JSX elements! Now it’s time to learn how to render them. To render a JSX expression means to make it appear onscreen.
- 11Let’s examine the code that you just wrote. Start in previous.js, on line 5, all the way to the left. You can see something called ReactDOM. What’s that? ReactDOM is the name of a JavaScript…
- 12Move to the right a little more, and you will see this expression: document.getElementById(‘app’) You just learned that ReactDOM.render() makes its first argument appear onscreen. But where…
- 13ReactDOM.render()’s first argument should evaluate to a JSX expression, it doesn’t have to literally be a JSX expression. The first argument could also be a variable, so long as that variable…
- 14One special thing about ReactDOM.render() is that it only updates DOM elements that have changed. That means that if you render the exact same thing twice in a row, the second render will do no…
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JSX
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