In ReactDOM. We can refactor the previous example into a functional component that accepts an array of numbers and outputs an unordered list of elements. When you run this code, you'll be given a warning that a key should be provided for list items. Keys should be included when creating lists of elements.
Let's assign a key to our list items inside numbers. Keys should be given to the elements inside the array to give the elements a stable identity. Keys serve as a hint to React but they don't get passed to your components.
If you need the same value in your component, pass it explicitly as a prop with a different name. Example: Incorrect key usage: Should not assign a key in this manner. Example: Correct key usage: Assigns key inside map function.
In React, you can create distinct components that encapsulate behavior you need. Then, you can render only the specific component you need, depending on the state of your application. Depending on the value of loggedIn the corresponding component will be rendered.
When a component has a conditional rendering, the appearance of the rendered component differs based on the condition. The article aims to be an exhaustive list of options for conditional renderings in React and best practices for these patterns. The most basic conditional rendering logic in React is done with a single if statement. Imagine you don't want to render something in your React componentbecause it doesn't have the necessary React props available. For instance, a List component in React shouldn't render the list HTML elements in a view if there is no list of items in the first place.
If the information from the props is null or undefined, the React component returns null in the conditional rendering. There, a React component that returns null instead of JSX will render nothing.
In this example, we have done the conditional rendering based on props, but the conditional rendering could be based on state and hooks too. Notice, how we didn't use the if statement inside the JSX yet but only outside before the return statement. Let's move on with the previous example to learn about if else statements in React. If there is no list, we render nothing and hide the HTML as we have seen before with the single if statement.
Even though the previous example shows you how to use if else statements in React, I suggest to use single if statements every time you want to guard your main return here: returning the list as a best practice:. This is way more readable than the previous if else conditional rendering. All the guards are neatly aligned as single if statements before the main return statement which can be interpreted as an implicit else statement too.
The parentheses around both implicit return statements in the ternary operator enable you to return a single or multiple HTML elements or React components from there. If it's just a single element though, you can omit the parentheses. Note: Sometimes you want to wrap multiple lines of elements with a div element as one block though.With React, we can build Single Page Applications that are dynamic and highly interactive. One way we fully utilize such interactivity is through conditional rendering.
Conditional rendering as a term describes the ability to render different UI markup based on certain conditions. In React-speak, it is a way to render different elements or components based on a condition. This concept is applied often in the following scenarios:. In this article, we examine seven 7 ways to implement such conditional rendering in React applications. Using the sample project, we will examine two ways if…else conditions may be used to implement conditional rendering in React.
To understand more about this behaviour, visit this link. Thus, we only need to execute the function within the JSX curly braces. In using this method, the component must be kept as simple as possible to avoid a wasted re-render of sibling or parent components.
As a result of this, we create a new functional component called AuthButton. Thus we import it in our index. The snippet above would achieve the same result but bloat the component unnecessarily while introducing performance issues as a result of constantly rerendering an unchanging component.
Element variables are simply variables that hold JSX elements.
Conditional Rendering in React using Ternaries and Logical AND
See demo below:. Notice how we conditionally assign values components to AuthButton and then we only have to render it neatly within our JSX. As shown previously, we can conditionally return different markup from a component based on set conditions using an if…else statement. The same could be achieved with a switch statement where we can specify the markup for various conditions.
See example below:.Sometimes, you want to render a UI component only if a certain condition is true. Which one you should choose depends on the situation. Sometimes, one approach may be the best tool for the job. Other times, it may come down to personal preference.
We have a main content section and a sidebar. This toolbar should be hidden from regular users. The most basic approach is to store an instance of our AdminToolbar component in a variable, but only if the isAdmin prop is true. React has no problem dealing with a null value in JSX. If the adminBar variable is nullReact will skip over it without rendering anything.
In the next example, we leave it up to the AdminToolbar component to decide on its own whether to render or not. Similarly, if the final expression were more complex than nullI feel like the mental overhead to understand how each expression fits into the ternary operator would become too high.
In my opinion, if the ternary operator needs to be split into multiple lines, our first approach with the variable and an if statement is a much better choice. For one-liners, though, the ternary operator is a pretty compelling option. Which approach do you prefer?
Lists & Conditional Rendering
Do you know about any other ways to conditionally render a component in React and JSX? If I forgot to include anything, let me know in the comments! Josh Tynjala is a frontend software developer, open source contributorkaraoke enthusiast, and he likes bowler hats. Josh develops Feathers UIa user interface component library for creative apps. He also built Logic. You should follow Josh on Twitter.
If the left-hand side is falsy, it returns that. Otherwise, it returns the right-hand side, whatever value it may happen to hold. The ternary operator is slightly longer, but more clear, in my opinion.This page contains a detailed API reference for the React component class definition. React lets you define components as classes or functions. Components defined as classes currently provide more features which are described in detail on this page. To define a React component class, you need to extend React.
Component :. The only method you must define in a React. Component subclass is called render. All the other methods described on this page are optional. We strongly recommend against creating your own base component classes. In React components, code reuse is primarily achieved through composition rather than inheritance. If you prefer to avoid it, you may use the create-react-class module or a similar custom abstraction instead. Take a look at Using React without ES6 to learn more.
You can use this lifecycle diagram as a cheat sheet. In the list below, commonly used lifecycle methods are marked as bold.
The rest of them exist for relatively rare use cases. These methods are called in the following order when an instance of a component is being created and inserted into the DOM:.
These methods are considered legacy and you should avoid them in new code:. An update can be caused by changes to props or state. These methods are called in the following order when a component is being re-rendered:.
These methods are called when there is an error during rendering, in a lifecycle method, or in the constructor of any child component. For a visual reference, check out this lifecycle diagram. The render method is the only required method in a class component. When called, it should examine this. If you need to interact with the browser, perform your work in componentDidMount or the other lifecycle methods instead. Keeping render pure makes components easier to think about.
The constructor for a React component is called before it is mounted. When implementing the constructor for a React. Component subclass, you should call super props before any other statement. Otherwise, this.
You should not call setState in the constructor. Instead, if your component needs to use local state, assign the initial state to this. Constructor is the only place where you should assign this. In all other methods, you need to use this. Avoid introducing any side-effects or subscriptions in the constructor. For those use cases, use componentDidMount instead.We have discussed how to create componentshow to render componentsusing proptypesusing states to store information and much more.
There may arise a situation when we want to render something based on some condition. Both the buttons have different functions so they will be separate components.
Now, the task is if a user is logged in then we will have to render the Logout component to display the logout button and if the user is not logged in then we will have to render the Login component to display the login button. That is to create multiple components and render them based on some conditions. This is also a kind of encapsulation supported by React. Let us now create a page in React which will have a Message and a Button. The value of this variable will change according to the click of the button by the user.
The Homepage component will render the Message component to display the message and it will also render one of the components among Login and Logout based on the value stored in isLoggedIn. The Message component will also return different messages based on the value of state isLoggedIn. It might happen sometimes that we may not want some components to render.REACT JS TUTORIAL #4 - State vs Props & Application Data
To prevent a component from rendering we will have to return null as its rendering output. Consider the below example:. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.
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Lists and Keys
I can find plenty of documentation and examples of conditionally including one component or another, but nothing which helps me in this use-case. Without the conditional, and adding all three of them works as expected. As Vivasaayi suggested, moving the logic to another function may be a good idea. However, if you want to have it all in one place, it could look something like this:. Learn more. Conditional with multiple React Components in class render method Ask Question. Asked 4 years, 3 months ago.
Active 4 years, 2 months ago. Viewed 2k times. I have a React class with a render method that includes 1 or 3 child components. Dmitry Shvedov 2, 4 4 gold badges 25 25 silver badges 41 41 bronze badges.
Jack Wild Jack Wild 1, 2 2 gold badges 19 19 silver badges 28 28 bronze badges. I think you forgot to set a colon between the 2 List elements, which makes React think that you return two root elements for one expression and that is considered invalid facebook.
Strange that it doesn't complain about the messed up expression though. I just noticed that as well Active Oldest Votes. You should wrap adjacent JSX elements in another element, like div. Moreover, I will suggest to move the rendering logic to another function to make it clear. Thanks, I have been doing that in other components so will refactor this one.
I tried wrapping them in another element, but I'd rather not pollute the DOM with additional wrappers if I can avoid it