React Developer Tools is a system that allows you to inspect a React Renderer, including the Component hierarchy, props, state, and more.
There are shells for Chrome (adding it to the Chrome devtools), Firefox, Atom/Nuclide, and as a standalone Electron app.
The official extensions represent the current stable release.
- Chrome extension
- Firefox extension
- Standalone app (coming soon)
If you inspect an element or launch the developer tools on a React page, you should see an extra tab called React in the inspector.
Check out For Hacking if you want to develop the Developer Tools or use a pre-prelease version.
- Arrow keys or hjkl for navigation
- Right click a component to show in elements pane, scroll into view, show source, etc.
- Use the search bar to find components by name
- A red collapser means the component has state/context
- Right-click to store as global variable
- Updates are highlighted
For changes that don't directly involve Chrome/Firefox/etc. APIs, there is a
"plain" shell that just renders the devtools into an html page along with a
TodoMVC test app. This is by far the quickest way to develop. Check out
the Readme.md in /shells/plain for info.
For other shells (Chrome, Firefox, etc.), see the respective directories in /shells.
The "React" tab won't show up if React can't communicate with the
devtools. When the page loads, the devtools sets a global named
__REACT_DEVTOOLS_GLOBAL_HOOK__, then React communicates with that
hook during initialization.
(In React 0.11 and older, it was necessary to expose a global called React
for the devtools to function.)
You can test this on the React website or by inspecting Facebook.
Currently iframes and Chrome apps/extensions are not inspectable.
Yes, but it's also tracing if a component may render.
In order to fully understand what counts as an "update", you need to understand how shouldComponentUpdate works.
Here "Trace React Updates" will draw a border around every node but C4 and C5. Why does it trace components that don't actually update? (via shouldComponentUpdate() -> false) This is a limitation of the system used to track updates, and will hopefully change in the future. It doesn't, however, trace the children of components that opt out, as there's no possibility of them updating. The higher the rate of updates happening per second the more the color changes from blue to red.
If you inspect a React element on the page using the regular Elements tab, then switch over to the React tab, that element will be automatically selected in the React tree.
What to do if the extension breaks.
- check the error console of devtools. Part of React Devtools runs scripts in the context of your page, and is vulnerable to misbehaving polyfills.
- open devtools out into a new window, and then hit the shortcut to open devtools again (cmd+option+j or ctrl+shift+j). This is the "debug devtools" debugger. Check the console there for errors.
- open
chrome://extensions, find react devtools, and click "background page" under "Inspected views". You might find the errors there.
To read more about the community and guidelines for submitting pull requests, please read the Contributing document.