JSX stands for JavaScript XML and is a syntax extension for JavaScript, commonly used with React. It allows you to write HTML-like code within JavaScript, making it easier to create and manage UI components in React.
Here’s a basic example of JSX:
React.createElement()
calls by tools like Babel.{}
) within JSX.Self-closing tags: In JSX, tags like <img />
or <input />
are self-closing, as opposed to HTML where you’d write <img></img>
.
Class vs className: In JSX, class
is written as className
to avoid conflicts with the reserved JavaScript keyword.
Let’s dive deeper into JSX and its key concepts, features, and how it works within React.
JSX is a syntax extension for JavaScript that allows you to write HTML-like code inside JavaScript. It’s mainly used with React to define what the UI should look like. When you use JSX, you can create React elements more intuitively, as if you are writing HTML directly in JavaScript.
However, JSX is not HTML—it is a syntactic sugar over JavaScript function calls. In the background, JSX is transformed into React.createElement()
function calls, which ultimately generate React elements.
React uses this function to create virtual DOM elements. JSX simplifies the process of writing and visualizing UI components in JavaScript.
You can embed any JavaScript expression inside curly braces {}
within JSX. This includes variables, functions, or even mathematical operations.
In the above examples, {name}
and {2 + 3}
are JavaScript expressions embedded within the JSX.
When you write JSX, React takes care of converting the JSX into React.createElement()
calls. This means React must be in scope for JSX to work correctly. Typically, you import React in your JavaScript files when you write JSX.
React elements are plain JavaScript objects that describe what you want to appear on the screen. React uses the virtual DOM to optimize updates to the actual DOM, making the UI more efficient.
React elements can be rendered with the ReactDOM.render()
method.
JSX is an expression, which means it can be assigned to variables, passed as arguments, and returned from functions.
In JSX, HTML attributes are written in camelCase instead of lowercase. For example:
class
becomes className
for
becomes htmlFor
style
is written as an object with camelCase properties instead of a string.In the style
attribute, you need to pass an object with key-value pairs instead of a string.
You can conditionally render JSX elements based on certain conditions using standard JavaScript logic, such as if
, else
, or ternary operators.
You can also use logical &&
operator for rendering elements conditionally:
To render lists in React, you can use JavaScript’s map()
function to iterate over an array and generate JSX elements. When rendering lists, keys are essential for efficient updates of the virtual DOM
Here, the key
prop helps React keep track of which items changed, added, or removed.
In some cases, you might want to return multiple elements from a component without adding extra nodes to the DOM. This is where fragments come in. Fragments allow you to group multiple elements without introducing a wrapper node.
You can also use React.Fragment
:
<img>
, <input>
, and <br>
don’t need a closing tag. In JSX, these tags must be self-closing: <img />
, <input />
, <br />
.onclick
in HTML becomes onClick
in JSX.className
instead of class
and htmlFor
instead of for
to avoid conflicts with JavaScript keywords.Since browsers don’t understand JSX natively, tools like Babel transpile JSX code into regular JavaScript before it can run in the browser. JSX code is ultimately compiled down into React.createElement
function calls.
For example, JSX:
Transpiles to:
Although JSX simplifies the development process, it doesn’t inherently impact performance. However, React’s virtual DOM ensures that only necessary updates are made to the actual DOM, which improves rendering performance.
JSX is a powerful and expressive tool that allows you to write React components in a way that closely resembles HTML. It makes the code more readable and declarative, especially for UI rendering. Understanding JSX is a fundamental step when learning React, and it’s essential for building modern web applications with this library.
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