React makes it easy to conditionally render components, elements, or sections of a User Interface. The conditional rendering feature is essential as it allows you to display content based on certain conditions.

One of the simplest and most commonly used patterns for conditional rendering in React is using the logical AND (&&) operator. This approach is concise and clean, making it a go-to choice for many React developers.

Conditional rendering allows you to decide whether or not to render an element or component based on a condition. The logical AND operator works efficiently due to its 'short-circuit behavior'.

Conditional rendering using && works in this pattern:

• If the condition before the && is true, the expression after the && will be rendered.
• If the condition is false, nothing is rendered.

Syntax

condition && expression

• condition: A boolean expression that evaluates to true or false.
• expression: The JSX or component that will be rendered if the condition is true.

Simply put, with short-circuiting using the && operator, the left-hand condition is evaluated first and if it's false, the right-hand side is ignored totally.

Short-circuiting with && is like deciding to open a door only if you confirm that the person knocking is someone you know. The first condition (checking if you know the person) must be true before you even consider opening the door (rendering). If you don’t know the person, you skip the step of opening the door altogether.

This analogy can be depicted as:

{isFriend && <p>Hello, welcome!</p>}

Here, you open the door (render the greeting) only if isFriend is true. If it's false, the door remains shut, and no further action is taken. This ensures you don't waste effort on unnecessary actions.

Example

Here is a simple example showing conditional rendering with &&:

function App() {
  const isUserLoggedIn = true; 

  return (
    <div>
      <h1>React Course</h1>
      {isUserLoggedIn && <p>Welcome back, User!</p>}
    </div>
  );
}

In this example:

• A variable called isUserLoggedIn is set to a boolean value of true.
• The component returns a JSX with a h1 and a message if the condition is true.
• The p element of "Welcome back, User!" would be displayed because the isUserLoggedIn is true.
• If isUserLoggedIn is set to false, no message would be displayed.

Checking for logged in users is a good use case of using conditional rendering.