react-devtools-inline

React DevTools implementation for embedding within a browser-based IDE (e.g. CodeSandbox, StackBlitz).

This is a low-level package. If you're looking for the standalone DevTools app, use the react-devtools package instead.

Usage

This package exports two entry points: a frontend (to be run in the main window) and a backend (to be installed and run within an iframe1).

The frontend and backend can be initialized in any order, but the backend must not be activated until the frontend initialization has completed. Because of this, the simplest sequence is:

1. Frontend (DevTools interface) initialized in the main window.
2. Backend initialized in an iframe.
3. Backend activated.

1 Sandboxed iframes are supported.

API

react-devtools-inline/backend

• initialize(contentWindow) - Installs the global hook on the window. This hook is how React and DevTools communicate. This method must be called before React is loaded.2
• activate(contentWindow) - Lets the backend know when the frontend is ready. It should not be called until after the frontend has been initialized, else the frontend might miss important tree-initialization events.

import { activate, initialize } from 'react-devtools-inline/backend';

// This should be the iframe the React application is running in.
const iframe = document.getElementById(frameID);
const contentWindow = iframe.contentWindow;

// Call this before importing React (or any other packages that might import React).
initialize(contentWindow);

// Initialize the frontend...

// Call this only once the frontend has been initialized.
activate(contentWindow);

2 The backend must be initialized before React is loaded. (This means before any import or require statements or <script> tags that include React.)

react-devtools-inline/frontend

• initialize(contentWindow) - Configures the DevTools interface to listen to the window the backend was injected into. This method returns a React component that can be rendered directly3.

import { initialize } from 'react-devtools-inline/frontend';

// This should be the iframe the backend hook has been installed in.
const iframe = document.getElementById(frameID);
const contentWindow = iframe.contentWindow;

// This returns a React component that can be rendered into your app.
// <DevTools {...props} />
const DevTools = initialize(contentWindow);

3 Because the DevTools interface makes use of several new React APIs (e.g. suspense, concurrent mode) it should be rendered using either ReactDOM.createRoot or ReactDOM.createSyncRoot. It should not be rendered with ReactDOM.render.

Examples

Configuring a same-origin iframe

The simplest way to use this package is to install the hook from the parent window. This is possible if the iframe is not sandboxed and there are no cross-origin restrictions.

import {
  activate as activateBackend,
  initialize as initializeBackend
} from 'react-devtools-inline/backend';
import { initialize as initializeFrontend } from 'react-devtools-inline/frontend';

// The React app you want to inspect with DevTools is running within this iframe:
const iframe = document.getElementById('target');
const { contentWindow } = iframe;

// Installs the global hook into the iframe.
// This must be called before React is loaded into that frame.
initializeBackend(contentWindow);

// React application can be injected into <iframe> at any time now...
// Note that this would need to be done via <script> tag injection,
// as setting the src of the <iframe> would load a new page (without the injected backend).

// Initialize DevTools UI to listen to the hook we just installed.
// This returns a React component we can render anywhere in the parent window.
const DevTools = initializeFrontend(contentWindow);

// <DevTools /> interface can be rendered in the parent window at any time now...
// Be sure to use either ReactDOM.createRoot()
// or ReactDOM.createSyncRoot() to render this component.

// Let the backend know the frontend is ready and listening.
activateBackend(contentWindow);

Configuring a sandboxed iframe

Sandboxed iframes are also supported but require more complex initialization.

iframe.html

import { activate, initialize } from "react-devtools-inline/backend";

// The DevTools hook needs to be installed before React is even required!
// The safest way to do this is probably to install it in a separate script tag.
initialize(window);

// Wait for the frontend to let us know that it's ready.
function onMessage({ data }) {
  switch (data.type) {
    case "activate-backend":
      window.removeEventListener("message", onMessage);

      activate(window);
      break;
    default:
      break;
  }
}

window.addEventListener("message", onMessage);

main-window.html

import { initialize } from "react-devtools-inline/frontend";

const iframe = document.getElementById("target");
const { contentWindow } = iframe;

// Initialize DevTools UI to listen to the iframe.
// This returns a React component we can render anywhere in the main window.
// Be sure to use either ReactDOM.createRoot()
// or ReactDOM.createSyncRoot() to render this component.
const DevTools = initialize(contentWindow);

// Let the backend know to initialize itself.
// We can't do this directly because the iframe is sandboxed.
// Only initialize the backend once the DevTools frontend has been initialized.
iframe.onload = () => {
  contentWindow.postMessage(
    {
      type: "activate-backend"
    },
    "*"
  );
};

Local development

You can also build and test this package from source.

Prerequisite steps

DevTools depends on local versions of several NPM packages1 also in this workspace. You'll need to either build or download those packages first.

1 Note that at this time, an experimental build is required because DevTools depends on the createRoot API.

Build from source

To build dependencies from source, run the following command from the root of the repository:

yarn build-for-devtools

Download from CI

To use the latest build from CI, run the following command from the root of the repository:

./scripts/release/download-experimental-build.js

Build steps

Once the above packages have been built or downloaded, you can watch for changes made to the source code and automatically rebuild by running:

yarn start

To test package changes, refer to the react-devtools-shell README.