In this situation it is likely that you're not returning your result correctly.įor our example we will be mapping our array of foods to some elements so we can show it to the user. We expect to see the or elements on screen with the data we map into them. Example ProblemĪ frustrating example can be seen when we map a data set to some elements or components. Whatever it is there are a few pitfalls we need to watch out for when it comes to returning our data otherwise we might be left scratching our heads. Perhaps we are filtering a data set down to a specific sub-set or mapping to the DOM. In React as we have already seen we are often iterating over some data. You could also use a package like nanoid that generates unique string id's for you. Instead we could create our key by combining the name property with the current date/time using the JavaScript Date object. See here for more information Reactjs - Reconciliation. It can negatively affect the state of the component. Often people use the index of the array as the key but this is not recommended for any set of data where positions in the list may change. If we didn't have a unique id we would need to have an alternative solution. Fortunately we have and id property we can use from our set of data. Often the data we are mapping comes from a fetch request and usually includes an id. To fix this all we have to do is pass a unique key to the element we are returning. foods is just an array of objects and it looks like this □ Here we will have a simple component that deconstructs foods from the prop object. Let's map some data before adding keys to our elements to see the problem in action. Keys should be given to the elements inside the array to give the elements a stable identity Example Problem Keys help React identify which items have changed, are added, or are removed. It should be a unique string which will distinguish it from its siblings that we are also mapping. Essentially it is just a special attribute to which we pass a string. When we do this without adding a key prop React will complain that each element is missing a key. This is often done using the function to pass data from each index of the array to the element or component through props. In React we often find ourselves with lists of data that we want to map into elements or components. Not cleaning up certain useEffect side-effectsġ) Forgetting to add keys with a list of elements.Forgetting to add keys with a list of elements.So let's not waste any time and take a look at our problems and how we can solve them □. They can be easily avoided in most situations and I would like to share them with you so you can spend less time debugging and more time writing code. Posting your app is a great way to get feedback regarding your work.When using the popular JavaScript library React there are some errors/problems that seem to pop up time and time again. Get Your Next Project Idea Here Got a project to show? Get an invite to our sub's chatroom, it's new! Talk in Real Time (tm)! Project Ideas Scrimba's React course by /u/mrborgen86./u/acemarke's suggested resources for learning React, JS, and more. Mods will remove such posts posted on other days. If you want to show off or need feedback on your portfolios, you should post on Sundays, and Sundays only. Therefore posts of NSFW React apps must link to source, not to the live NSFW app. We ask that NSFW posts nevertheless focus on the technology rather than the content. links to NSFW apps built with React) but try not to be prudes. Please link some source code (or if not possible, we understand, link some live demo or codepen so that people can try you out and learn from you) 6. We're all here to learn from you, but can't learn very much from a video recording. Demos should link source code or live demos If you need further guidelines on spam, see Reddit's guidelines on Spam. Per Reddit guidelines for self-promotion, you are definitely welcome to promote your own content as part of your participation in this community, but if you repeatedly post low quality crap you will be banned. Telling people to "get out" of the industry or that they are not good enough in some shape or form is a bannable offense. Reasoned criticism of React or any other library is welcome, but spare us your rants. Polite or Constructive criticism is welcome but don't rag on other people's work or attempts to improve themselves. Interested in building mobile apps using React Native? Check out /r/reactnative! Rules 1. A community for learning and developing web applications using React by Facebook.
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