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If screen.getPrimaryDisplay() is undefined, the call is usually running in the renderer process (or DevTools) instead of Electron’s main process, or it runs before Electron has emitted ready. Import screen in the main process and call it after app.whenReady() resolves.
The documented fix
Electron classifies the screen module as main-process only. The smallest working pattern is:
const { app, BrowserWindow, screen } = require('electron/main')
app.whenReady().then(() => {
const primaryDisplay = screen.getPrimaryDisplay()
const { width, height } = primaryDisplay.workAreaSize
const mainWindow = new BrowserWindow({ width, height })
mainWindow.loadURL('https://electronjs.org')
})This follows Electron’s documented example. Adapt the window options and page URL to your application. The important parts are the process, import, and timing: the call is in the main process, and it executes only after app.whenReady().
Why the value is undefined
The line is running in the wrong process
Renderer JavaScript executes inside a browser window. DevTools code executes in that same renderer context. Neither context owns Electron’s main-process screen module. If the failing file is loaded by a window, preload, or DevTools console, move the actual display query to the main process.
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Electron’s screen documentation also warns that, in the renderer and DevTools, window.screen is a reserved DOM property. Consequently, writing let { screen } = require('electron') there does not give you Electron’s screen API. A browser’s window.screen describes the web page’s screen-related properties; it is not the Electron screen module.
The call runs before app readiness
The screen module cannot be used until the app emits its ready event. Calling it at top level, before the event, can fail even when the code is in the correct file. Put the call inside app.whenReady().then(...), or run it from a code path that you know executes after readiness. Electron exposes app.isReady() when you need to check the current state.
Move display information across the process boundary
A renderer should not import or call Electron’s main-only screen API. Instead, have the main process obtain the display and return only the values the user interface needs. The exact IPC arrangement depends on your security model; the following CommonJS example keeps the screen query in the main process and exposes one narrowly scoped operation through a preload script.
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Main process
const { app, BrowserWindow, ipcMain, screen } = require('electron/main')
const path = require('node:path')
let mainWindow
app.whenReady().then(() => {
ipcMain.handle('display:get-primary-work-area', () => {
const { workArea, workAreaSize, bounds, scaleFactor } = screen.getPrimaryDisplay()
return { workArea, workAreaSize, bounds, scaleFactor }
})
mainWindow = new BrowserWindow({
width: 1000,
height: 700,
webPreferences: {
preload: path.join(__dirname, 'preload.js'),
contextIsolation: true,
nodeIntegration: false
}
})
mainWindow.loadFile('index.html')
})Register the handler after readiness so a renderer cannot ask for display data before Electron has initialized the module. The returned object contains a snapshot; if monitors are added, removed, or repositioned later, request a new snapshot rather than assuming the old values remain current.
Preload script
const { contextBridge, ipcRenderer } = require('electron')
contextBridge.exposeInMainWorld('displayAPI', {
getPrimaryWorkArea: () => ipcRenderer.invoke('display:get-primary-work-area')
})Renderer code
document.querySelector('#read-display').addEventListener('click', async () => {
try {
const display = await window.displayAPI.getPrimaryWorkArea()
document.querySelector('#output').textContent =
JSON.stringify(display, null, 2)
} catch (error) {
document.querySelector('#output').textContent = error.message
}
})This pattern prevents the renderer from trying to resolve screen.getPrimaryDisplay itself. If your project already has an IPC or preload abstraction, add an equivalent method there instead of exposing the entire Electron API.
Check your project in the right order
- Identify the executing file. Follow the stack trace to the JavaScript file that contains the failing expression. Determine whether that file is your main entry point, a preload script, a renderer bundle, or DevTools input.
- Confirm the import. In the main process, compare your import with the documented
require('electron/main')pattern. Verify that the variable you callscreenis the imported module, not a local variable or the browser’swindow.screen. - Confirm readiness. Move the call into
app.whenReady(). If you use a helper function, call that helper from the readiness callback rather than invoking it while the module is being loaded. - Check the installed Electron version. Read the version from the project’s package configuration and compare its API documentation with the rolling documentation for a different release. Behavior or import guidance can differ between versions.
- Reduce the case. Temporarily replace your window setup with the short documented example. If that works, restore your application code incrementally; the first change that reintroduces the error identifies the incorrect process or lifecycle path.
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Python
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timeout=90,
)
r.raise_for_status()
open("shot.webp", "wb").write(r.content)Node.js
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Common errors and their fixes
| Symptom | Likely cause | Fix |
|---|---|---|
screen is undefined in a renderer bundle |
The code is executing in the renderer, where Electron’s main-process module is unavailable. | Move the query to the main process and return the result through preload and IPC. |
let { screen } = require('electron') produces an unexpected value |
In renderer or DevTools, screen collides with the reserved DOM property window.screen. |
Do not destructure Electron’s screen module in that context. Use a main-process handler. |
| The import exists, but the call fails during startup | The call occurs before the app’s ready event. |
Put it inside app.whenReady() or after a readiness check. |
| The minimal example works but the application does not | A wrapper, preload boundary, renamed variable, or alternate entry point changes the process or call order. | Compare the working example with your actual entry file and restore changes one at a time. |
| The error remains after moving the call | The installed Electron release, import syntax, or stack trace may differ from the assumptions above. | Record the Electron version, exact import, executing file, complete error text, and stack trace, then consult the documentation for that release. |
Lifecycle and display details that affect results
Readiness is not window creation
You can query the primary display after the app is ready and before creating a BrowserWindow; the documented example does exactly that. Creating a window first does not make the screen module available earlier. Conversely, creating a window does not automatically make renderer code authorized to call the main-only module.
Use the right display fields
screen.getPrimaryDisplay() returns Electron’s Display object for the primary display. Its workAreaSize excludes areas reserved by system UI, while bounds describes the display rectangle. Choose the field that matches your goal: sizing a window for usable desktop space is different from measuring the full display bounds.
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The value returned by getPrimaryDisplay() represents the display state at the time of the call. If your application supports monitor changes or resolution changes, request fresh data when your own display-change handling runs. Do not cache the initial dimensions indefinitely.
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Final verification checklist
- The failing expression is executed by the main process, not a renderer or DevTools.
- The main entry imports
screenusing the syntax appropriate for the installed Electron version. - The query runs after
app.whenReady()resolves or after thereadyevent. - Renderer code receives values through your existing preload/IPC boundary instead of importing
screen. - Your test records the Electron version and the complete stack trace if the minimal pattern still fails.
Frequently Asked Questions
Does `getPrimaryDisplay()` return the monitor where my window is currently located?
No. It returns the `Display` object Electron designates as the primary display. If you need the display containing a particular window, use the appropriate display-selection logic in the main process rather than assuming the primary display is the window’s display.
Can a renderer use the browser’s `window.screen` instead?
It can read the browser DOM property, but that is a different API and does not provide Electron’s `Display` object. Use the main-process query when you need Electron display bounds, work-area dimensions, or scale information.
Quick Recap
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