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※ Download: Each child in an array or iterator should have a unique key prop.
This warning comes when you don't add a key to your list items. As per react js Docs - Keys help React identify which items have changed, are added, or are removed. So maybe if you look at it...
Component { constructor props, context { super props, context ; this. It was passed a child from App.
Comments - As per react js Docs - Keys help React identify which items have changed, are added, or are removed. In our case, we're lucky, because we have an ID.
I have a problem with the key props in a React JS component. Check the render method of Login. It was passed a child from App. App component is as follows : import React from 'react'; import Header from '.. Component { constructor props { super props ; this. UPDATE LoginForm component : import React from 'react'; import Link from 'react-router'; import TextInput from '.. Component { constructor props, context { super props, context ; this. But each time you iterate over an array you have to set the key prop to each of the resulting DOM element as React needs it to optimize the re-rendering. The reason behind this warning is that you have not passed 'key' property. React uses this property for optimizing the rendering process as in when something changes in React, a re-render will occur only for what all has changed. If our children are dynamic and in case they get shuffled with random functions or new components are introduced in the beginning of an array, the re-render is likely to get messed up. So, assigning this 'key' property helps us make sure that the state and identity of our components is maintained through multiple renders. The importance of key is beautifully explained. I certainly appreciate you updating your answer, but please actually post the code in your answer: links can and do go dead. If the code example is one that you got from somewhere else as opposed to created yourself, by all means add the link for attribution but still post the code inside your actual answer.
Most often you would use IDs from your data as keys So the updated solution to this will be: return this. If we open up the developer tools, we're going to get this warning from React, saying each child in an array or iterator should have a unique key prop. It was passed a child from App. Could you try it. As per react js Docs - Keys help React identify which items have changed, are added, or are removed. To do this, it needs to keep track using a key. See for more information. The grape now actually has 2, when it had 3 before. Child keys must be unique; when two children share a key, only the first child will be used.