Conditional Rendering

Your components will often need to display different things depending on different conditions. In React, you can conditionally render JSX using JavaScript syntax like if statements, &&, and ? : operat

In React, you can create distinct components that encapsulate behavior you need. Then, you can render only some of them, depending on the state of your application.

Conditional rendering in React works the same way conditions work in JavaScript. Use JavaScript operators like if or the conditional operator to create elements representing the current state, and let React update the UI to match them.

Conditionally returning JSX

Let’s say you have a PackingList component rendering several Items, which can be marked as packed or not:

Notice that some of the Item components have their isPacked prop set to true instead of false. You want to add a checkmark (✔) to packed items if isPacked={true}.

You can write this as an if/else statement like so:

if (isPacked) {
  return <li className="item">{name} ✔</li>;
}
return <li className="item">{name}</li>;

If the isPacked prop is true, this code returns a different JSX tree. With this change, some of the items get a checkmark at the end:

Try editing what gets returned in either case, and see how the result changes!

Notice how you’re creating branching logic with JavaScript’s if and return statements. In React, control flow (like conditions) is handled by JavaScript.

Conditionally returning nothing with null

In some situations, you won’t want to render anything at all. For example, say you don’t want to show packed items at all. A component must return something. In this case, you can return null:

if (isPacked) {
  return null;
}
return <li className="item">{name}</li>;

If isPacked is true, the component will return nothing, null. Otherwise, it will return JSX to render.

In practice, returning null from a component isn’t common because it might surprise a developer trying to render it. More often, you would conditionally include or exclude the component in the parent component’s JSX. Here’s how to do that!

Conditionally including JSX

In the previous example, you controlled which (if any!) JSX tree would be returned by the component. You may already have noticed some duplication in the render output:

<li className="item">{name} ✔</li>

is very similar to

<li className="item">{name}</li>

Both of the conditional branches return <li className="item">...</li>:

if (isPacked) {
  return <li className="item">{name} ✔</li>;
}
return <li className="item">{name}</li>;

While this duplication isn’t harmful, it could make your code harder to maintain. What if you want to change the className? You’d have to do it in two places in your code! In such a situation, you could conditionally include a little JSX to make your code more DRY.

Conditional (ternary) operator (? :)

JavaScript has a compact syntax for writing a conditional expression — the conditional operator or “ternary operator”.

Instead of this:

if (isPacked) {
  return <li className="item">{name} ✔</li>;
}
return <li className="item">{name}</li>;

You can write this:

return (
  <li className="item">
    {isPacked ? name + ' ✔' : name}
  </li>
);

You can read it as “if isPacked is true, then (?) render name + ' ✔', otherwise (:) render name”.

Now let’s say you want to wrap the completed item’s text into another HTML tag, like <del> to strike it out. You can add even more newlines and parentheses so that it’s easier to nest more JSX in each of the cases:

This style works well for simple conditions, but use it in moderation. If your components get messy with too much nested conditional markup, consider extracting child components to clean things up. In React, markup is a part of your code, so you can use tools like variables and functions to tidy up complex expressions.

Logical AND operator (&&)

Another common shortcut you’ll encounter is the JavaScript logical AND (&&) operator. Inside React components, it often comes up when you want to render some JSX when the condition is true, or render nothing otherwise. With &&, you could conditionally render the checkmark only if isPacked is true:

return (
  <li className="item">
    {name} {isPacked && '✔'}
  </li>
);

You can read this as “if isPacked, then (&&) render the checkmark, otherwise, render nothing”.

Here it is in action:

A JavaScript && expression returns the value of its right side (in our case, the checkmark) if the left side (our condition) is true. But if the condition is false, the whole expression becomes false. React considers false as a “hole” in the JSX tree, just like null or undefined, and doesn’t render anything in its place.

Pitfall

Don’t put numbers on the left side of &&.

To test the condition, JavaScript converts the left side to a boolean automatically. However, if the left side is 0, then the whole expression gets that value (0), and React will happily render 0 rather than nothing.

For example, a common mistake is to write code like messageCount && <p>New messages</p>. It’s easy to assume that it renders nothing when messageCount is 0, but it really renders the 0 itself!

To fix it, make the left side a boolean: messageCount > 0 && <p>New messages</p>.

Conditionally assigning JSX to a variable

When the shortcuts get in the way of writing plain code, try using an if statement and a variable. You can reassign variables defined with let, so start by providing the default content you want to display, the name:

let itemContent = name;

Use an if statement to reassign a JSX expression to itemContent if isPacked is true:

if (isPacked) {
  itemContent = name + " ✔";
}

Curly braces open the “window into JavaScript”. Embed the variable with curly braces in the returned JSX tree, nesting the previously calculated expression inside of JSX:

<li className="item">
  {itemContent}
</li>

This style is the most verbose, but it’s also the most flexible. Here it is in action:

If you’re not familiar with JavaScript, this variety of styles might seem overwhelming at first. However, learning them will help you read and write any JavaScript code — and not just React components! Pick the one you prefer for a start, and then consult this reference again if you forget how the other ones work.

Recap

• In React, you control branching logic with JavaScript.

• You can return a JSX expression conditionally with an if statement.

• You can conditionally save some JSX to a variable and then include it inside other JSX by using the curly braces.

• In JSX, {cond ? <A /> : <B />} means “if cond, render <A />, otherwise <B />”.

• In JSX, {cond && <A />} means “if cond, render <A />, otherwise nothing”.

• The shortcuts are common, but you don’t have to use them if you prefer plain if.