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Is there any way to get logs of which all React components get rendered or rerendered when any event/action is performed. I just want to check whether any unwanted React component is getting rerendered. I know we could achieve this by adding consoles in render function, componentWillReceiveProps or componentWillUpdate. But I have number of components in my webapp. Adding console statements in each component would be a mess. Is there a better way?
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React DevTools lets you highlight renders under Components -> View Settings -> Highlight updates when components render. This will show you the virtual renders. If you want to see native re-renders, you can do so in the Chrome DevTools, under the three-dot menu on the right -> More tools -> Rendering -> Paint flashing.
Re-render happens when React needs to update the app with some new data. Usually, this happens as a result of a user interacting with the app or some external data coming through via an asynchronous request or some subscription model.
The simplest way to check how many times React components render is by using the “Highlight updates when components render” option in React DevTools.
It deduces the changes of your data by running the reducer function you provide, and returns the next state that corresponds to every action dispatched. React Redux then optimizes component rendering and makes sure that each component re-renders only when the data it needs change.
A nice option is to visualise React components in the chrome timeline. This lets you see which components exactly get mounted, updated, and unmounted and how much time they take relative to each other. That feature was added as part of the release of React 15.4.0. You can take a look at the official blogpost to get a better insight, but summing up, those are the steps to get it up and running:
Load your app with ?react_perf in the query string (for example, http://localhost:3000/?react_perf).
Open the Chrome DevTools Timeline tab and press Record.
Perform the actions you want to profile. Don't record more than 20 seconds or Chrome might hang.
Stop recording.
React events will be grouped under the User Timing label.
After that, you will get a cool visual representation of mounting, updating and unmounting of your different components over time
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In addition to rauliyohmc answer. Profiling tool he described is really helpful and powerful, but if your task is just checking if there are unnecessary re-renders (i.e. ones which did not lead to DOM changes) you can use nice and simple react-addons-perf tool. It has printWasted method which will provide you info about wasted re-renders.
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