What is JSX?
JSX is not a requirement for using React, but it's highly recommended because it simplifies the code and makes it more intuitive. With JSX, we can create React elements and components using a syntax that's similar to the HTML we're already familiar with.
Understanding the Syntax of JSX
Basic Syntax Rules
In the above code, we have a React component named App. Inside the JSX return statement, we have a div with a className of "App". Inside this div, we have an h1 element that renders the text "Hello World".
Embedding Expressions in JSX
In the above example, we have a variable name that holds the string 'React'. Inside our JSX code, we embed this variable inside the h1 tag using curly braces. When this component is rendered, it will display "Hello React".
JSX expressions can also be used for attribute values. For example, we can dynamically set the className of an element based on a variable or function.
In the above code, we use a ternary expression inside the className attribute to conditionally add the 'active' class based on the isActive variable.
JSX vs HTML: The Differences
While JSX may look like HTML at first glance, there are several key differences between the two that are important to understand when working with React.
JSX Attributes vs HTML Attributes
In HTML, we use attributes to provide additional information about HTML elements. JSX also uses attributes, but there are some important differences.
In the above JSX code, we use className instead of class, htmlFor instead of for, and tabIndex instead of tabindex.
JSX Tags vs HTML Tags
JSX tags are very similar to HTML tags, but there are some key differences.
In HTML, tags can be left open if they are self-closing. However, in JSX, all tags must be closed. If a tag doesn't have any children, it must be self-closed using a / before the closing >.
In the above JSX code, both the input and br tags are self-closed.
Another difference is that JSX tags can represent HTML elements, but they can also represent user-defined React components. This allows us to compose complex UIs from smaller, reusable pieces.
In the above JSX code, Header is a user-defined React component that is used inside the App component.
Components and Props in JSX
React is built around the concept of components. Components are reusable pieces of code that return a React element to be rendered to the DOM. This section'll delve into components and how to use props in JSX.
A React component can be as simple as a function that returns a JSX element. Here's an example:
In the above code, Welcome is a function component that returns a JSX element. We can use this component in other parts of our application just like we use HTML tags.
Components allow us to split the UI into independent, reusable pieces. Each component is responsible for rendering a part of the UI, and a complex UI can be broken down into smaller, easier-to-manage components.
Using Props in JSX
Props (short for properties) are how components talk to each other. They are inputs to a React component and they are passed as attributes in JSX.
Props are read-only and a component should never modify its own props. They should always be passed down from the parent component.
Here's an example of using props in a React component:
In the above code, Welcome is a function component that takes props as an argument. Inside the component, we use props.name to access the name prop. In the App component, we use the Welcome component and pass a name prop to it.
Defining and Using JSX Children
Children in JSX are defined between the opening and closing tags of an element. Here's an example:
In the above code, the div element has two children: an h1 element and a p element.
In the above code, we have a variable name that holds the string 'React'. Inside our JSX code, we embed this variable as a child of the h1 element using curly braces. When this component is rendered, it will display "Hello, React!".
Conditional Rendering in JSX
In React, we often need to display different UIs for different conditions. This is known as conditional rendering. In this section, we'll explore how to use if statements, ternary expressions, and the logical && operator for conditional rendering in JSX.
If Statements and Ternary Expressions
In JSX, we can't use if statements directly inside the curly braces. However, we can use if statements inside the component function body or ternary expressions directly inside the curly braces.
Here's an example of using an if statement inside a component function:
In the above code, we use an if statement to check if the name prop is true. If it is, we render a greeting with the name. If it's not, we render a greeting for a guest.
We can also use ternary expressions directly inside the curly braces for inline conditional rendering:
In the above code, we use a ternary expression to check if the name prop is truthy. If it is, we render the name. If it's not, we render 'guest'.
Inline If with Logical && Operator
Another method for conditional rendering in JSX is using the logical && operator. This is useful when we want to conditionally render an element based on a truthy value.
Here's an example:
JSX and Styles
Styling is a crucial part of any web application. In React, we can apply styles to JSX elements in two ways: inline styles and CSS classes. In this section, we'll explore both methods.
Inline Styles in JSX
In the above code, we define a style object with three properties: color, backgroundColor, and padding. We then pass this object to the style attribute of the div element.
CSS Classes and JSX
In addition to inline styles, we can also use CSS classes to style our JSX elements. As mentioned earlier, we use the className attribute in JSX instead of the class attribute in HTML.
Here's an example:
In the above code, we use the className attribute to apply the "App" CSS class to the div element.
It's important to note that CSS classes in React work the same way as in regular HTML. The styles for the class should be defined in a separate CSS file and imported into the React component.
Create Efficient React Applications With JSX!
By understanding JSX in depth, the differences between JSX and HTML, how to use components and props, how to define and use children, how to perform conditional rendering, and how to apply styles in JSX, developers can create efficient and maintainable React applications.
Moreover, by following the best practices for using JSX in React, such as keeping JSX expressions short and readable, always closing tags, and using parentheses to avoid the pitfalls of automatic semicolon insertion, developers can write clean, efficient, and bug-free JSX code.