<. We're a place where coders share, stay up-to-date and grow their careers. However, it's perfectly safe to use it with TypeScript because you get a quick overview of what props are being passed and get an error immediately if an unexpected property occurs. Built on Forem the open source software that powers DEV and other inclusive communities. In this case, nothing gets rendered and React outputs a warning message. Sucrase playground link. necessary (so React can spread them out as if they were positional args to This component is only responsible for outputting the name and the surname of the user to the screen. Get monthly updates about new articles, cheatsheets, and tricks. For example, in development mode, key validation accompanies an iteration. Yeah I'm using React. Generator object should not be used as a child of React element. ***> wrote: A CSS, HTML junkie who codes with Carnatic BGM, sips coffee while planning Marathons, and does pushups while watching Darth Vader reign. I don't know why Babel chokes on this, though I've seen a higher rate of Image source: Christina Morillo/@divinetechygirl on Pexels. For further actions, you may consider blocking this person and/or reporting abuse. Updated on Jan 13, 2021. Where each property needs to be passed as a single prop value you could use the spread operator supported for arrays in ES6 to pass down all your values. This means we need to further inspect the code plus it can lead to unnecessary complexity when debugging. The component will now look like this. right? There are a few things to remember about to get the most out of it. Once unsuspended, arikaturika will be able to comment and publish posts again. https://facebook.github.io/jsx/ includes it: Some history here: facebook/jsx#57 . The firs example that came into my head was the CSS styles example but our variables can virtually contain anything we want. I am using destructuring to get the individual props so we can get rid of the props. 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We also use React.memo() to ensure that the User component is not unnecessarily re-rendered with the App. Later attributes override previous ones. Purchase includes access to 30+ courses, 240+ premium tutorials, 120+ hours of videos, source files and certificates. TypeScript didn't implement that check, it seems. It's also useful when you're transplanting `children` from Today we will learn why Spread Operator is great, but better avoided when passing a set of props in React. See how both the App and User components are wrapped into the borders when they're updated, which means that both are refreshed when the button is clicked, which is wrong because the User component shouldn't be refreshed. Developing web and mobile applications while learning new techniques everyday, Apply your Swift and SwiftUI knowledge by building real, quick and various applications from scratch, An extensive series of tutorials covering advanced topics related to React hooks, with a main focus on backend and logic to take your React skills to the next level, Concurrency, swipe actions, search feature, AttributedStrings and accessibility were concepts discussed at WWDC21. notation: We can easily see that the more props we want to pass, the messier the code becomes. https://babeljs.io/repl#?babili=false&browsers=&build=&builtIns=false&spec=false&loose=false&code_lz=FAYw9gdgzgLgBAMTgXjgCgJQoHxwDwCG2A3gHTkDaAugL54D0RA3EA&debug=false&forceAllTransforms=false&shippedProposals=false&circleciRepo=&evaluate=false&fileSize=false&timeTravel=false&sourceType=module&lineWrap=true&presets=es2015%2Creact%2Cstage-2&prettier=false&targets=&version=7.3.3, https://github.com/notifications/unsubscribe-auth/AAAb2V-Vv--U8HfQQBqxWfTL8e9voKBEks5vQAlPgaJpZM4bGMwh, Fix implementation of JSX spread children, Fix implementation of JSX spread children (. Successfully merging a pull request may close this issue. Are you sure you want to hide this comment? Our army protects all Europe from the occupiers and it needs help now to restrain one of the biggest armies in the world. It's not always obvious what the props we're passing have inside. This rule was introduced in DeepScan 1.34.0. My impression is Babel parses and recognizes it but intentionally disallows it for React, since they're worried that beginners will use it for dynamic arrays when really they should be specifying keys. DEV Community A constructive and inclusive social network for software developers. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Today we learned why using Spread Operator to pass props to the child component in React can be considered antipattern: In any case, Spread Operator makes your code look more elegant and shorter, but remember to use it wisely. With this article, we are starting a new chapter called "React Antipatterns", which will consist of a few articles showing how not to write code in React and explaining why. class span Site made with React, Gatsby, Netlify and Contentful. Support Ukraine Donate to support families affected by the crisis, Learn how to make use of the spread operator. It will become hidden in your post, but will still be visible via the comment's permalink. Generator objects are the return values of generator functions. Have a question about this project? But I think that restriction is something a linter should do (and a team should be allowed to opt in and out of), so I think it's fine to just allow and transform the syntax as specified in Sucrase. and only accessible to Arika O. array but know it's actually static and unchanging, so that keys are not Well occasionally send you account related emails. Receive all new posts directly to your e-mail, No spam, only quality content twice a week, Let me know what you think about this article, Contact me and let's discuss any opportunities, // { name: "John", surname: "Doe", age: 18 }, // {"0": "s", "1": "t", "2": "r", "3": "i", "4": "n", "5": "g"}, // Prints ["John", "Andrew", "Ann", "Rose"], // Prints "{ minusOne: -1, minusTwo: -2, one: 1, two: 2 }", // Spreads array of numbers to a function arguments, // Prints {name: "John", surname: "Doe", age: 18}, // Prints {name: "John", surname: "Doe", age: 22}, To find out what is being passed, you need to scroll to where, If you forget that Spread Operator is used and add another property to, You can accidentally pass more props than necessary, It's hard to tell which props are actually being passed unless you use TypeScript. Another case is that you also can use spread operator to pass only parts of props to children components, then you can use destructuring syntax from props again. I think React wants you to pass an array there so it knows to check that you're using keys properly. bugs in Babel than TSC so far since the switch in create react app 2.0 Important Note: For simplicity, we could have omitted curly braces and return in the User component, but we will keep them for now. Looks like the original argument for adding it was for non-React use cases. It's very useful when children components need lots of props but not want pass them one by one. By clicking Sign up for GitHub, you agree to our terms of service and The usage is equivalent to saying "Pass all these props to this component", and we complain that all properties are really passed, weird, isn't it?

Please, donate a small amount. ([random example](, On Fri, Feb 22, 2019 at 7:14 AM Alan Pierce ***@***. React Warning: Using Generators as children is unsupported and will likely yield unexpected results because enumerating a generator mutates it. Sign in The look of our application is far from fancy, but the topic is not about the design, is it? Let's call it ExampleComponentName. Made with love and Ruby on Rails. FWIW, Babel (with the React transform) throws an exception, saying "Spread children are not supported in React" (repl). Are you using something other than React? You can see this happening in the example below: But what if we want, for example, to render a second child component and apply certain CSS styles to it? Luckily, there's something called the spread operator - or spread attributes - that we can use, which only takes a few seconds to code! Once unpublished, this post will become invisible to the public If arikaturika is not suspended, they can still re-publish their posts from their dashboard. Antipatterns, just like patterns, have been around for a long time and it's worth learning and remembering them to avoid code smell. My FWIW, Babel (with the The order is important. You may convert it to an array with Array.from() or the [spread] operator before rendering. What we could do instead is store all the styles in an object and pass it from parent to child using the spread operator. Learn how. Iterating an already iterated Generator object results in an empty iteration. That's certainly what I'd expect. You can avoid this problem by converting the Generator object to an array using Array.from() or array spread operator like [generatorObject]. This rule applies when a Generator object is used as a child of React element. Like so: And our child component will access the properties of that object like this: I sometimes use this method for passing props but I'm not a big fan of it. DEV Community 2016 - 2022. Let's say we have a parent component called App which renders a child component called ExampleComponentDate. We all try to be consistent with our way of teaching step-by-step, providing source files and prioritizing design in our courses. I just released a fix for this in 3.10.0. here are many ways to write bad code in React that are well known and should either be avoided or at least known about. You signed in with another tab or window. Already on GitHub? While it's perfectly fine to use Spread Operator, you need to be very careful, as it's easy to accidentally pass unnecessary props, resulting in extra re-renders and greatly impacting the performance of the application. Keep in mind you might need to polyfill these features for older browsers. Let's create an application that contains two components: App and User. This drawback only applies to applications that do not use TypeScript. understanding of this syntax is that it's for places where you have an View with compliant examples side by side, View with noncompliant examples side by side, export class Hello extends React.Component {, {hello()} {/* REACT_BAD_CHILD_GENERATOR alarm because generator object is used as a child. This modified text is an extract of the original, How to setup a basic webpack, react and babel environment, Detecting the type of Children components, React Boilerplate [React + Babel + Webpack], React.createClass vs extends React.Component. With you every step of your journey. Donate to support families affected by the crisis. If you have props as an object in React and want to pass them to the child component, you can use the Spread Operator to do so: You can even combine it with explicit props passing: Or override a property passed with the Spread Operator: It seems like using Spread Operator only brings benefits, shortening the code and making it more sophisticated, but that's not quite true. one place to another. Once suspended, arikaturika will not be able to comment or publish posts until their suspension is removed.

Once unpublished, all posts by arikaturika will become hidden and only accessible to themselves. Interesting, I actually hadn't seen that syntax. Let's change the App component code a bit to avoid using Spread Operator, but to explicitly pass the name and surname props: See how only one border, wrapping the entire App component appears. Let's look at some usage examples for this operator. Unlike other iterable objects such as array, Generator objects can be iterated only once. */}. createElement). First, let's learn or remember what Spread Operator does and why it's awesome. Regardless, I think it's within Sucrase's scope to just compile it and let other tools do the error checking, so this certainly seems reasonable to implement. privacy statement. It is, nevertheless, very useful when children components need lots of props but we do not want to pass them one by one. FWIW this is syntax that Typescript supported. Ukraine was invaded by Russia in the early morning of 24.02.2022, explosions thundered in Ukrainian cities, many civilians died, tens of millions are affected. Learning how not to write code is as important as learning best practices and design patterns. During rendering, React may perform multiple iterations of iterable objects. In React, passing props from parent to children components and using them is pretty straight forward. Let's imagine our styles are stored inside multiple variables in the parent and we want to use them inside the second child. Most of the time we learn how to write code, we memorize best practices, design patterns, clean code principles, and that's perfectly fine, but learning how not to write code is no less important. The text was updated successfully, but these errors were encountered: Interesting, I actually hadn't seen that syntax. supported in React" (repl They can still re-publish the post if they are not suspended. The child component will display a date we set in the parent component, so to be able to use it, it needs to get it from one level up (in this case) through props. Download the videos and assets to refer and learn offline without interuption. Let's take a closer look at App.jsx, specifically at the following lines of code: We know that the User component expects only two properties - name and surname, but we passed the entire state and added an extra counter, which causes the User component to be unnecessarily re-rendered since the counter isn't used, remember? If you have many props in an object, using Spread Operator makes it easier to pass them to the child component, but it's easy to lose control of them: The claim that using Spread Operator is antipattern is not 100% accurate. Looks like TypeScript is transforming it to React.createElement('div', null, a, b), which seems like it ruins the point of spread children. The Spread Operator is used to access all the elements within an Iterable: Important Note: the Spread Operator makes a shallow copy of the Iterable. If you are not familiar with the "Highlight updates when components render" feature of the React dev tools, you can add console.log() to both components and check the console. Let's say we have a component that takes a lot of props. We pass our props like so: And our child component will use them like in the code below. Personally, I like to think of this as an antipattern because it makes me triple check the code and make sure Spread Operator is needed in the particular component, which means that I use it wisely. Templates let you quickly answer FAQs or store snippets for re-use. Posted on May 3, 2020 Remember that the properties of the object that you pass in are copied onto the component's props. The second drawback of this approach comes into play when you pass a lot of props to the child component - it's easy to get lost and spend a few minutes guessing what exactly is being passed, unless you use TypeScript and explicitly define what is expected by the child component. React transform) throws an exception, saying "Spread children are not