| # Dev Overlay | |
| ## Project Structure | |
| - `next-devtools/dev-overlay/` - The UI that Next.js developers can interact with in development. | |
| - `next-devtools/server/` - Code that runs in the Next.js development server. | |
| - `next-devtools/shared/` - Anything that doesn't fit in | |
| - `next-devtools/userspace/` - Code that runs in the user's application. | |
| Modules in `dev-overlay/` are isolated from the rest of the source. Any stateful module will not share state with e.g. `userspace/`. Stateful modules in `shared/` cannot be used to pass data from `dev-overlay/` to `userspace/` or vice versa. | |
| `userspace/` code can send messages to `dev-overlay/` via the `dispatcher` imported from `next/dist/compiled/next-devtools`. | |
| Keep processing in `userspace/` to a minimum and prefer deriving data in `dev-overlay/`. | |
| ## Development | |
| The dev overlay leverages [Shadow DOM](https://developer.mozilla.org/en-US/docs/Web/API/Web_components/Using_shadow_DOM) to insert the dev overlay into the client without affecting the user's application through encapsulation from CSS. | |
| ### Local Development | |
| Next.js uses [Storybook](https://storybook.js.org) to develop UI components in the dev overlay. | |
| To run the dev overlay locally, you can run the following command: | |
| ```bash | |
| pnpm storybook | |
| ``` | |
| This will start the Storybook server at `http://localhost:6006`. | |
| ### Styling | |
| Next.js direcly injects CSS into the DOM via `<style>` tag. The styles will not affect the user's application as the [styles are encapsulated](https://developer.mozilla.org/en-US/docs/Web/API/Web_components/Using_shadow_DOM#encapsulation_from_css) from the rest of the application. | |
| > [!TIP] | |
| > While Shadow DOM provides style encapsulation, the root element (i.e., `<nextjs-portal>`) can still inherit styles from parent elements like `<body>` or `<html>`. Direct styling on these parent elements (e.g., `body { contain: layout; }`) will affect the dev overlay. | |
| Write CSS in template literals alongside your components. It is recommended to use the class names that are unique within the dev overlay to avoid conflicts. You can use `data-nextjs-` data attributes to target the elements in the dev overlay. | |
| ```tsx | |
| export function Component() { | |
| return ( | |
| <div className="some-unique-class-name"> | |
| <h1>Hello, Next.js!</h1> | |
| </div> | |
| ) | |
| } | |
| export const COMPONENT_NAME_STYLES = ` | |
| .some-unique-class-name { | |
| background-color: red; | |
| } | |
| ` | |
| ``` | |
| > [!IMPORTANT] | |
| > Use the `css()` util that minifies and removes the comments before injecting to the `<style>` tag. | |
| The exported `COMPONENT_NAME_STYLES` can be used in the styles entrypoint (i.e., `ComponentStyles`) of the dev overlay to inject into the `<style>` tag. | |
| ```tsx | |
| import { COMPONENT_NAME_STYLES } from './component' | |
| export function ComponentStyles() { | |
| return ( | |
| <style> | |
| {css` | |
| // ... | |
| ${COMPONENT_NAME_STYLES} | |
| `} | |
| </style | |
| ) | |
| } | |
| ``` | |
| ### Dark Theme | |
| The dev overlay implements a dark theme automatically by system preferences. Users can manually toggle between light and dark themes via the DevTools Indicator preferences panel. | |
| To make changes to the dark theme, you can edit the [`ui/styles/dark-theme.tsx`](./ui/styles/dark-theme.tsx) file. | |