According to the Hooks documentation: Don’t call Hooks inside loops, conditions, or nested functions. It is called during the mounting and updating phases of the component lifecycle. Let’s review another technique that can help improve the code. The essential idea is that changing the position of the components due to conditional rendering can cause a reflow that will unmount/mount the components of the app. Logical && (Short Circuit Evaluation with &&) Short circuit evaluation is a technique used to ensure … This usually happens with the useEffect hook. We only want to render a h2 for the subtitle if it exists. For example, here’s how you define one in TypeScript: JavaScript doesn’t support enums natively, but we can use an object to group all the properties of the enum and freeze that object to avoid accidental changes. You can check out our, Node.js installed locally, which you can do by following. You can conditionally assign elements or components to these variables outside the JSX and only render the variable within JSX. The first one uses an if/else block to show/hide the SubHeader component: The second one uses the short circuit operator (&&) to do the same: Open the Inspector and click on the button a few times. In the same way, there’s an EditComponent: Now the render method can look like this: There are libraries like jsx-control-statements that extend JSX to add conditional statements like: This library is actually a Babel plugin, so the above code is translated to: Or the Choose tag, which is used for more complex conditional statements: These libraries provide more advanced components, but if we need something like a simple if/else, we can use a solution similar to Michael J. Ryan’s in the comments for this issue: Now that the save/edit functionality is encapsulated in two components, we can also use enum objects to render one of them, depending on the state of the application. Previously, the Login and Logout buttons were displayed. Element variables are variables that hold JSX elements. Ternary operator is a shorter form of the ‘if-else’ condition. This post was originally published several years ago, before the stable release of the Hooks API, and we just updated it a few months back. Final Words. The needs and conventions of your project may require you to adopt approaches that do not follow these recommendations. In this example, we'll render a Card component that takes a title prop and optionally a subtitle prop. There are numerous ways to do this in React, depending on the situation. React creators make our life easier and by default such variables are ignored in a JSX tree. This code produces the same result as the renderAuthButton() approach. The logical && helps you specify that an action should be taken only on one condition, otherwise, it would be ignored entirely. Continue your learning with Higher Order Components and Conditional Rendering with HOCs. You can consult the, An understanding of importing, exporting, and rendering React components. Applying this to our example, we can declare an enum object with the two components for saving and editing: And use the mode state variable to indicate which component to show. This is also a kind of encapsulation supported by React. We can do it like this in react. Next, add some methods for handling input text and then save and edit events: Now, for the render method, check the mode state property to either render an edit button or a text input and a save button, in addition to the saved text: Here’s the complete Fiddle to try it out: An if/else block is the easiest way to solve the problem, but I’m sure you know this is not a good implementation. And replace the contents with the following lines of code: Then, run the application from your terminal window: And interact with the application in your browser: Each of the conditional rendering approaches will build upon this code. There’s more than one way to use conditional rendering in React. It can also be applied in different parts of the component. In this tutorial, we are going to learn about how to loop through array of elements in a react. For example, you could use the ternary operator this way: Better yet, you could use a short-circuit &&: You could also encapsulate the rendering of the child elements in a method and use an if or switch statement to decide what to return: Today, most experienced React developers use Hooks to write components. One important thing to keep in mind when returning null, however, is that even though the component doesn’t show up, its lifecycle methods are still fired. Conditional rendering in React in using the && operator In the examples presented above, we’re not using the else part of our conditionals to render something different. Rendering Multiple Components You can build collections of elements and include them in JSX using curly braces {}. LogRocket is like a DVR for web apps, recording literally everything that happens on your site. But it doesn’t support loops or conditional expressions directly (although the addition of conditional expressions has been discussed before). Let’s consider if you were to attempt to use an if…else statement in the render() method: Warning: This is an example of code that will not work properly. What is Conditional Rendering? The answer is by using fragments. For that reason, sometimes you might want to use other techniques, like immediately invoked functions. Sign up for Infrastructure as a Newsletter. We use an if with our condition and return the element to be rendered. I’ll talk more about the performance implications of conditional rendering later. Ok lets learn them. render() The render() method is the only required method in the component lifecycle. Thanks for keeping us honest. If the user is logged out, it will display a Login button. But conditional rendering? https://blog.hackages.io/conditionally-wrap-an-element-in-react-a8b9a47fab2 Generally, this is how you define and execute (at a later point) a function: But if you want to execute the function immediately after it is defined, you have to wrap the whole declaration in parentheses (to convert it to an expression) and execute it by adding two more parentheses (passing any arguments the function may take). Conditional rendering is a term to describe the ability to render different user interface (UI) markup if a condition is true or false. Short circuit evaluation is a technique used to ensure that there are no side effects during the evaluation of operands in an expression. React.js is designed to make the process of building modular, reusable user interface components simple and intuitive. Hub for Good You can build Single Page Applications (SPA) that are dynamic and highly interactive with React. React conditional render multiple elements. Ternary operator. In React, you can have expressions like the following: If showHeader evaluates to true, the component will be returned by the expression. Instead, always use Hooks at the top level of your React function. In JSX, you are able to use JavaScript code with markup to render dynamic values within your application. An if…else statement will execute the actions contained in the if block when the condition is satisfied. Thereafter, we can use “event.target.name.” to call out the names and let the function handle it. After all, we’re using React — the recommended approaches are to split up the logic of your app into as many components as possible and to use functional programming instead of imperative programming. Let’s observe the example below. Rendering with && Let's look at one of the most common cases: conditionally rendering a React element based on whether a specific prop exists or not. Open the App.js file in your code editor, scroll down to the render() method and make the following highlighted code changes: This is the process of creating an extracted function. This can also be written in a slightly more concise manner using an arrow function: Certain libraries expose functionality to extend JSX, making it possible to implement conditional rendering directly with JSX. When you look at the console, however, you’ll see that componentDidUpdate is always called regardless of the value returned by render. At some point, when building a React component, you'll run into a situation where you need to apply a class based on some condition. In functional programming, the Either type is commonly used as a wrapper to return two different values. It’s 2020, function components with hooks are not an “alternative” way. React render requires you to return a value. Do not bloat your component unnecessarily within the, The size of markup to be rendered conditionally, Which would be more intuitive and readable. While developing an application in React or any other JS library/ framework, it is a common use case to show or hide elements based on certain conditions. Maybe in this simple example, the performance improvement is insignificant, but when working when big components, there can be a difference. 4277. I’m going to start by creating a SaveComponent: As properties, it receives everything it needs to work. This code extracts the logic from JSX into a function renderAuthButton. Let us now create a page in React which will have a Message and a Button. React render is one of the many component lifecycles that a React component goes through. Using a Normal if The easiest way is to use a normal if inside our component code and return inside and outside the if. You can decide which one is best for your situation based on: And, all things being equal, always favor simplicity and readability. : }. An understanding of JavaScript variables and functions. Write for DigitalOcean Do not change the position of components arbitrarily in order to prevent components from unmounting and remounting unnecessarily. 1. Working on improving health and education, reducing inequality, and spurring economic growth? You get paid; we donate to tech nonprofits. Your article is a great resource for beginner React developers, but also confusing, because you use class components. Next, revisit App.js and modify it to use the new component: This is the process of creating an extracted functional component. Possible Solutions: 1- Either you need to wrap all the elements in a div or any other wrapper Then, you can render only some of them, depending on the state of your application. You can conditionally render jsx elements by using two methods. The conditional (ternary) operator is the only JavaScript operator that takes three operands. This is what we call Conditional Rendering in ReactJS. Rendering with If / Else Inline Conditionals Logical && Ternary Operator Oftentimes when building with React, we will want to display different elements depending on the state of the application. But when they do, you’ll need a good understanding of how React works with the virtual DOM and a few tricks to optimizing performance. A higher-order component (HOC) is a function that takes an existing component and returns a new one with some added functionality: Applied to conditional rendering, a HOC could return a different component than the one passed based on some condition: There’s an excellent article about HOCs by Robin Wieruch that digs deeper into conditional renderings with higher-order components. Then, you can render only some of them, depending on the state of your application. You get paid, we donate to tech non-profits. However, the ternary operator doesn’t always look better. Since the function won’t be called in any other place, you can drop the name: In React, you use curly braces to wrap an IIFE, put all the logic you want inside it (if/else, switch, ternary operators, etc. By following this rule, you ensure that Hooks are called in the same order each time a component renders. Create a component with the following state: You’ll use one property for the saved text and another for the text that is being edited. As the name implies, immediately invoked function expressions (IIFEs) are functions that are executed immediately after they are defined — there’s no need to call them explicitly. You can’t put a condition that could prevent the hook from being called every time the component is rendered, like this: You have to put the condition inside the Hook: As with many things in programming, there are many ways to implement conditional rendering in React. If you’re interested in monitoring and tracking Redux state for all of your users in production, try LogRocket. We’ll start with the most naive implementation using an if/else block and build it from there. : ; How to Install Node.js and Create a Local Development Environment, this article on high performing conditionals in React, Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. https://thinkster.io/tutorials/iterating-and-rendering-loops-in-react Below, we loop through the numbers array using the JavaScript map () function. eherrera.net, Immediately invoked function expressions (IIFEs), Deciding how to implement conditional rendering in React, immediately invoked function expressions (IIFEs), optimizing conditional rendering in React, 11 alternative frameworks to Ruby on Rails, 11 database drivers and ORMs for Rust that are ready for production, Node.js, Express.js, and MySQL: A step-by-step REST API example, Managing network connection status in React Native, It doesn’t work with multiple/different conditions, How comfortable you are with JavaScript, JSX, and advanced React concepts (like HOCs). For this article, I’m going to borrow the concepts of the EitherComponent. For example, when trying the Fiddle that renders the empty
element, if you open the Inspector tab, you’ll see how the
element under the root is always updated: Unlike the case when null is returned to hide the component, where that
element is not updated when the Edit button is clicked: Learn more about reconciliation in React, which basically refers to how React updates the DOM elements and how the diffing algorithm works. But here, I’m going to do something a bit different to show you how you can go from an imperative solution to more declarative and functional solutions. As shown previously, you can conditionally return different markup from a component based on set conditions using an if…else statement. Consider we have an array of users, we need to loop them using for loop and render the elements into the dom. They are THE way to go and classes are unnecessary for the examples you show. Let’s apply it to the example so you can see this in action. Open your application in your web browser. Our component has an all-or-nothing behavior, where nothing is rendered in place of the drawer if the expanded state property is false. For example, here’s how the logic to render the save/edit button could look with an IIFE: Sometimes, an IFFE might seem like a hacky solution. b : c) As a final option, we can take advantage of the shorthand nature of the … In this article, you examined seven ways to implement conditional rendering in React applications. If you want to hide a component, you can make its render method return null, so there’s no need to render an empty (and different) element as a placeholder. One of such libraries is JSX Control Statements. Take, for example, the following Fiddle, which implements a counter with two components: The Number component only renders the counter for even values; otherwise, null is returned. In this React tutorial, we’ll look into some basic expression rendering methods in the components JSX template including dynamic looping over the Object to create a list, using conditional expressions lie if; else and Switch case to manage multiple conditions. Handling authentication and authorization. Change only the markup that is concerned with the conditional rendering. Start with using create-react-app to generate a React App: Next, open the App.js file in your code editor. Conditional rendering means to add or remove elements from the dom if a particular condition is true. For situations where there are two expected outcomes, an, For situations where there are more than two outcomes, a. For instance, based on some logic it can either return a list of items or a text that says "Sorry, the list is empty". if. Why not just use constants? Use JavaScript operators like if or the conditional operator to create elements representing the current state, and let React update the UI to … This may either be null, undefined or JSX markup. DigitalOcean makes it simple to launch in the cloud and scale up as you grow – whether you’re running one virtual machine or ten thousand. JSX uses curly braces ({ and }) to signify expressions that need to be interpreted prior to rendering. Here is how you can do it. This is how you can use forms to React. Consider a complex, nested set of conditions: This can become a mess pretty quickly. Like books, movies, and still trying many things. A third property will indicate if you are in edit or view mode. Now, let’s consider using a second short circuit evaluation for the Login button: This code would render the right button based on the value of isLoggedIn.
