React JSX
What is JSX?
JSX stands for JavaScript XML.
JSX allows us to write HTML in React.
JSX makes it easier to write and add HTML in React.
Coding JSX
JSX allows us to write HTML elements in JavaScript and place them in the DOM
without any createElement() and/or
appendChild() methods.
JSX converts HTML tags into react elements.
You are not required to use JSX, but JSX makes it easier to write React applications.
Here are two examples. The first uses JSX and the second does not:
Example 1
JSX:
const myElement = <h1>I Love JSX!</h1>;
const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(myElement);
Example 2
Without JSX:
const myElement = React.createElement('h1', {}, 'I do not use JSX!');
const root = ReactDOM.createRoot(document.getElementById('root'));
root.render(myElement);
As you can see in the first example, JSX allows us to write HTML directly within the JavaScript code.
JSX is an extension of the JavaScript language based on ES6, and is translated into regular JavaScript at runtime.
Expressions in JSX
With JSX you can write expressions inside curly braces { }.
The expression can be a React variable, or property, or any other valid JavaScript expression. JSX will execute the expression and return the result:
Example
Execute the expression 5 + 5:
const myElement = <h1>React is {5 + 5} times better with JSX</h1>;
Inserting a Large Block of HTML
To write HTML on multiple lines, put the HTML inside parentheses:
Example
Create a list with three list items:
const myElement = (
<ul>
<li>Apples</li>
<li>Bananas</li>
<li>Cherries</li>
</ul>
);
One Top Level Element
The HTML code must be wrapped in ONE top level element.
So if you like to write two paragraphs, you must put them inside a
parent element, like a div element.
Example
Wrap two paragraphs inside one DIV element:
const myElement = (
<div>
<p>I am a paragraph.</p>
<p>I am a paragraph too.</p>
</div>
);
JSX will throw an error if the HTML is not correct, or if the HTML misses a parent element.
Alternatively, you can use a "fragment" to wrap multiple lines. This will prevent unnecessarily adding extra nodes to the DOM.
A fragment looks like an empty HTML tag: <></>.
Example
Wrap two paragraphs inside a fragment:
const myElement = (
<>
<p>I am a paragraph.</p>
<p>I am a paragraph too.</p>
</>
);
Elements Must be Closed
JSX follows XML rules, and therefore HTML elements must be properly closed.
JSX will throw an error if the HTML is not properly closed.
Attribute class = className
The class attribute is a much used attribute
in HTML, but since JSX is rendered as JavaScript, and the
class keyword is a reserved word in JavaScript,
you are not allowed to use it in JSX.
Use attribute className instead.
JSX solved this by using className instead.
When JSX is rendered, it translates className
attributes into class attributes.
Example
Use attribute className instead of
class in JSX:
const myElement = <h1 className="myclass">Hello World</h1>;
Conditions - if statements
React supports if statements, but not inside JSX.
To be able to use conditional statements in JSX, you should put the if
statements outside of the JSX, or you could use a ternary expression instead:
Option 1:
Write if statements outside of the JSX code:
Example
Write "Hello" if x is less than 10, otherwise "Goodbye":
const x = 5;
let text = "Goodbye";
if (x < 10) {
text = "Hello";
}
const myElement = <h1>{text}</h1>;
Option 2:
Use ternary expressions instead:
Example
Write "Hello" if x is less than 10, otherwise "Goodbye":
const x = 5;
const myElement = <h1>{(x) < 10 ? "Hello" : "Goodbye"}</h1>;
Note that in order to embed a JavaScript expression inside JSX,
the JavaScript must be wrapped with curly braces, {}.