electron

session

Manage browser sessions, cookies, cache, proxy settings, etc.

Process: Main

The session module can be used to create new Session objects.

You can also access the session of existing pages by using the session property of WebContents, or from the session module.

const { BrowserWindow } = require('electron')

const win = new BrowserWindow({ width: 800, height: 600 })
win.loadURL('http://github.com')

const ses = win.webContents.session
console.log(ses.getUserAgent())

Methods

The session module has the following methods:

session.fromPartition(partition[, options])

Returns Session - A session instance from partition string. When there is an existing Session with the same partition, it will be returned; otherwise a new Session instance will be created with options.

If partition starts with persist:, the page will use a persistent session available to all pages in the app with the same partition. if there is no persist: prefix, the page will use an in-memory session. If the partition is empty then default session of the app will be returned.

To create a Session with options, you have to ensure the Session with the partition has never been used before. There is no way to change the options of an existing Session object.

Properties

The session module has the following properties:

session.defaultSession

A Session object, the default session object of the app.

Class: Session

Get and set properties of a session.

Process: Main
This class is not exported from the 'electron' module. It is only available as a return value of other methods in the Electron API.

You can create a Session object in the session module:

const { session } = require('electron')
const ses = session.fromPartition('persist:name')
console.log(ses.getUserAgent())

Instance Events

The following events are available on instances of Session:

Event: ‘will-download’

Returns:

Emitted when Electron is about to download item in webContents.

Calling event.preventDefault() will cancel the download and item will not be available from next tick of the process.

const { session } = require('electron')
session.defaultSession.on('will-download', (event, item, webContents) => {
  event.preventDefault()
  require('got')(item.getURL()).then((response) => {
    require('fs').writeFileSync('/somewhere', response.body)
  })
})

Event: ‘extension-loaded’

Returns:

Emitted after an extension is loaded. This occurs whenever an extension is added to the “enabled” set of extensions. This includes:

Event: ‘extension-unloaded’

Returns:

Emitted after an extension is unloaded. This occurs when Session.removeExtension is called.

Event: ‘extension-ready’

Returns:

Emitted after an extension is loaded and all necessary browser state is initialized to support the start of the extension’s background page.

Event: ‘preconnect’

Returns:

Emitted when a render process requests preconnection to a URL, generally due to a resource hint.

Event: ‘spellcheck-dictionary-initialized’

Returns:

Emitted when a hunspell dictionary file has been successfully initialized. This occurs after the file has been downloaded.

Event: ‘spellcheck-dictionary-download-begin’

Returns:

Emitted when a hunspell dictionary file starts downloading

Event: ‘spellcheck-dictionary-download-success’

Returns:

Emitted when a hunspell dictionary file has been successfully downloaded

Event: ‘spellcheck-dictionary-download-failure’

Returns:

Emitted when a hunspell dictionary file download fails. For details on the failure you should collect a netlog and inspect the download request.

Event: ‘select-hid-device’

Returns:

Emitted when a HID device needs to be selected when a call to navigator.hid.requestDevice is made. callback should be called with deviceId to be selected; passing no arguments to callback will cancel the request. Additionally, permissioning on navigator.hid can be further managed by using ses.setPermissionCheckHandler(handler) and ses.setDevicePermissionHandler(handler)`.

const { app, BrowserWindow } = require('electron')

let win = null

app.whenReady().then(() => {
  win = new BrowserWindow()

  win.webContents.session.setPermissionCheckHandler((webContents, permission, requestingOrigin, details) => {
    if (permission === 'hid') {
      // Add logic here to determine if permission should be given to allow HID selection
      return true
    }
    return false
  })

  // Optionally, retrieve previously persisted devices from a persistent store
  const grantedDevices = fetchGrantedDevices()

  win.webContents.session.setDevicePermissionHandler((details) => {
    if (new URL(details.origin).hostname === 'some-host' && details.deviceType === 'hid') {
      if (details.device.vendorId === 123 && details.device.productId === 345) {
        // Always allow this type of device (this allows skipping the call to `navigator.hid.requestDevice` first)
        return true
      }

      // Search through the list of devices that have previously been granted permission
      return grantedDevices.some((grantedDevice) => {
        return grantedDevice.vendorId === details.device.vendorId &&
              grantedDevice.productId === details.device.productId &&
              grantedDevice.serialNumber && grantedDevice.serialNumber === details.device.serialNumber
      })
    }
    return false
  })

  win.webContents.session.on('select-hid-device', (event, details, callback) => {
    event.preventDefault()
    const selectedDevice = details.deviceList.find((device) => {
      return device.vendorId === '9025' && device.productId === '67'
    })
    callback(selectedPort?.deviceId)
  })
})

Event: ‘hid-device-added’

Returns:

Emitted when a new HID device becomes available. For example, when a new USB device is plugged in.

This event will only be emitted after navigator.hid.requestDevice has been called and select-hid-device has fired.

Event: ‘hid-device-removed’

Returns:

Emitted when a HID device has been removed. For example, this event will fire when a USB device is unplugged.

This event will only be emitted after navigator.hid.requestDevice has been called and select-hid-device has fired.

Event: ‘select-serial-port’

Returns:

Emitted when a serial port needs to be selected when a call to navigator.serial.requestPort is made. callback should be called with portId to be selected, passing an empty string to callback will cancel the request. Additionally, permissioning on navigator.serial can be managed by using ses.setPermissionCheckHandler(handler) with the serial permission.

const { app, BrowserWindow } = require('electron')

let win = null

app.whenReady().then(() => {
  win = new BrowserWindow({
    width: 800,
    height: 600
  })

  win.webContents.session.setPermissionCheckHandler((webContents, permission, requestingOrigin, details) => {
    if (permission === 'serial') {
      // Add logic here to determine if permission should be given to allow serial selection
      return true
    }
    return false
  })

  // Optionally, retrieve previously persisted devices from a persistent store
  const grantedDevices = fetchGrantedDevices()

  win.webContents.session.setDevicePermissionHandler((details) => {
    if (new URL(details.origin).hostname === 'some-host' && details.deviceType === 'serial') {
      if (details.device.vendorId === 123 && details.device.productId === 345) {
        // Always allow this type of device (this allows skipping the call to `navigator.serial.requestPort` first)
        return true
      }

      // Search through the list of devices that have previously been granted permission
      return grantedDevices.some((grantedDevice) => {
        return grantedDevice.vendorId === details.device.vendorId &&
              grantedDevice.productId === details.device.productId &&
              grantedDevice.serialNumber && grantedDevice.serialNumber === details.device.serialNumber
      })
    }
    return false
  })

  win.webContents.session.on('select-serial-port', (event, portList, webContents, callback) => {
    event.preventDefault()
    const selectedPort = portList.find((device) => {
      return device.vendorId === '9025' && device.productId === '67'
    })
    if (!selectedPort) {
      callback('')
    } else {
      callback(selectedPort.portId)
    }
  })
})

Event: ‘serial-port-added’

Returns:

Emitted after navigator.serial.requestPort has been called and select-serial-port has fired if a new serial port becomes available. For example, this event will fire when a new USB device is plugged in.

Event: ‘serial-port-removed’

Returns:

Emitted after navigator.serial.requestPort has been called and select-serial-port has fired if a serial port has been removed. For example, this event will fire when a USB device is unplugged.

Instance Methods

The following methods are available on instances of Session:

ses.getCacheSize()

Returns Promise<Integer> - the session’s current cache size, in bytes.

ses.clearCache()

Returns Promise<void> - resolves when the cache clear operation is complete.

Clears the session’s HTTP cache.

ses.clearStorageData([options])

Returns Promise<void> - resolves when the storage data has been cleared.

ses.flushStorageData()

Writes any unwritten DOMStorage data to disk.

ses.setProxy(config)

Returns Promise<void> - Resolves when the proxy setting process is complete.

Sets the proxy settings.

When mode is unspecified, pacScript and proxyRules are provided together, the proxyRules option is ignored and pacScript configuration is applied.

You may need ses.closeAllConnections to close currently in flight connections to prevent pooled sockets using previous proxy from being reused by future requests.

The proxyRules has to follow the rules below:

proxyRules = schemeProxies[";"<schemeProxies>]
schemeProxies = [<urlScheme>"="]<proxyURIList>
urlScheme = "http" | "https" | "ftp" | "socks"
proxyURIList = <proxyURL>[","<proxyURIList>]
proxyURL = [<proxyScheme>"://"]<proxyHost>[":"<proxyPort>]

For example:

The proxyBypassRules is a comma separated list of rules described below:

ses.resolveProxy(url)

Returns Promise<string> - Resolves with the proxy information for url.

ses.forceReloadProxyConfig()

Returns Promise<void> - Resolves when the all internal states of proxy service is reset and the latest proxy configuration is reapplied if it’s already available. The pac script will be fetched from pacScript again if the proxy mode is pac_script.

ses.setDownloadPath(path)

Sets download saving directory. By default, the download directory will be the Downloads under the respective app folder.

ses.enableNetworkEmulation(options)

Emulates network with the given configuration for the session.

// To emulate a GPRS connection with 50kbps throughput and 500 ms latency.
window.webContents.session.enableNetworkEmulation({
  latency: 500,
  downloadThroughput: 6400,
  uploadThroughput: 6400
})

// To emulate a network outage.
window.webContents.session.enableNetworkEmulation({ offline: true })

ses.preconnect(options)

Preconnects the given number of sockets to an origin.

ses.closeAllConnections()

Returns Promise<void> - Resolves when all connections are closed.

Note: It will terminate / fail all requests currently in flight.

ses.disableNetworkEmulation()

Disables any network emulation already active for the session. Resets to the original network configuration.

ses.setCertificateVerifyProc(proc)

Sets the certificate verify proc for session, the proc will be called with proc(request, callback) whenever a server certificate verification is requested. Calling callback(0) accepts the certificate, calling callback(-2) rejects it.

Calling setCertificateVerifyProc(null) will revert back to default certificate verify proc.

const { BrowserWindow } = require('electron')
const win = new BrowserWindow()

win.webContents.session.setCertificateVerifyProc((request, callback) => {
  const { hostname } = request
  if (hostname === 'github.com') {
    callback(0)
  } else {
    callback(-2)
  }
})

NOTE: The result of this procedure is cached by the network service.

ses.setPermissionRequestHandler(handler)

Sets the handler which can be used to respond to permission requests for the session. Calling callback(true) will allow the permission and callback(false) will reject it. To clear the handler, call setPermissionRequestHandler(null). Please note that you must also implement setPermissionCheckHandler to get complete permission handling. Most web APIs do a permission check and then make a permission request if the check is denied.

const { session } = require('electron')
session.fromPartition('some-partition').setPermissionRequestHandler((webContents, permission, callback) => {
  if (webContents.getURL() === 'some-host' && permission === 'notifications') {
    return callback(false) // denied.
  }

  callback(true)
})

ses.setPermissionCheckHandler(handler)

Sets the handler which can be used to respond to permission checks for the session. Returning true will allow the permission and false will reject it. Please note that you must also implement setPermissionRequestHandler to get complete permission handling. Most web APIs do a permission check and then make a permission request if the check is denied. To clear the handler, call setPermissionCheckHandler(null).

const { session } = require('electron')
const url = require('url')
session.fromPartition('some-partition').setPermissionCheckHandler((webContents, permission, requestingOrigin) => {
  if (new URL(requestingOrigin).hostname === 'some-host' && permission === 'notifications') {
    return true // granted
  }

  return false // denied
})

ses.setDevicePermissionHandler(handler)

Sets the handler which can be used to respond to device permission checks for the session. Returning true will allow the device to be permitted and false will reject it. To clear the handler, call setDevicePermissionHandler(null). This handler can be used to provide default permissioning to devices without first calling for permission to devices (eg via navigator.hid.requestDevice). If this handler is not defined, the default device permissions as granted through device selection (eg via navigator.hid.requestDevice) will be used. Additionally, the default behavior of Electron is to store granted device permision through the lifetime of the corresponding WebContents. If longer term storage is needed, a developer can store granted device permissions (eg when handling the select-hid-device event) and then read from that storage with setDevicePermissionHandler.

const { app, BrowserWindow } = require('electron')

let win = null

app.whenReady().then(() => {
  win = new BrowserWindow()

  win.webContents.session.setPermissionCheckHandler((webContents, permission, requestingOrigin, details) => {
    if (permission === 'hid') {
      // Add logic here to determine if permission should be given to allow HID selection
      return true
    } else if (permission === 'serial') {
      // Add logic here to determine if permission should be given to allow serial port selection
    }
    return false
  })

  // Optionally, retrieve previously persisted devices from a persistent store
  const grantedDevices = fetchGrantedDevices()

  win.webContents.session.setDevicePermissionHandler((details) => {
    if (new URL(details.origin).hostname === 'some-host' && details.deviceType === 'hid') {
      if (details.device.vendorId === 123 && details.device.productId === 345) {
        // Always allow this type of device (this allows skipping the call to `navigator.hid.requestDevice` first)
        return true
      }

      // Search through the list of devices that have previously been granted permission
      return grantedDevices.some((grantedDevice) => {
        return grantedDevice.vendorId === details.device.vendorId &&
              grantedDevice.productId === details.device.productId &&
              grantedDevice.serialNumber && grantedDevice.serialNumber === details.device.serialNumber
      })
    } else if (details.deviceType === 'serial') {
      if (details.device.vendorId === 123 && details.device.productId === 345) {
        // Always allow this type of device (this allows skipping the call to `navigator.hid.requestDevice` first)
        return true
      }
    }
    return false
  })

  win.webContents.session.on('select-hid-device', (event, details, callback) => {
    event.preventDefault()
    const selectedDevice = details.deviceList.find((device) => {
      return device.vendorId === '9025' && device.productId === '67'
    })
    callback(selectedPort?.deviceId)
  })
})

ses.clearHostResolverCache()

Returns Promise<void> - Resolves when the operation is complete.

Clears the host resolver cache.

ses.allowNTLMCredentialsForDomains(domains)

Dynamically sets whether to always send credentials for HTTP NTLM or Negotiate authentication.

const { session } = require('electron')
// consider any url ending with `example.com`, `foobar.com`, `baz`
// for integrated authentication.
session.defaultSession.allowNTLMCredentialsForDomains('*example.com, *foobar.com, *baz')

// consider all urls for integrated authentication.
session.defaultSession.allowNTLMCredentialsForDomains('*')

ses.setUserAgent(userAgent[, acceptLanguages])

Overrides the userAgent and acceptLanguages for this session.

The acceptLanguages must a comma separated ordered list of language codes, for example "en-US,fr,de,ko,zh-CN,ja".

This doesn’t affect existing WebContents, and each WebContents can use webContents.setUserAgent to override the session-wide user agent.

ses.isPersistent()

Returns boolean - Whether or not this session is a persistent one. The default webContents session of a BrowserWindow is persistent. When creating a session from a partition, session prefixed with persist: will be persistent, while others will be temporary.

ses.getUserAgent()

Returns string - The user agent for this session.

ses.setSSLConfig(config)

Sets the SSL configuration for the session. All subsequent network requests will use the new configuration. Existing network connections (such as WebSocket connections) will not be terminated, but old sockets in the pool will not be reused for new connections.

ses.getBlobData(identifier)

Returns Promise<Buffer> - resolves with blob data.

ses.downloadURL(url)

Initiates a download of the resource at url. The API will generate a DownloadItem that can be accessed with the will-download event.

Note: This does not perform any security checks that relate to a page’s origin, unlike webContents.downloadURL.

ses.createInterruptedDownload(options)

Allows resuming cancelled or interrupted downloads from previous Session. The API will generate a DownloadItem that can be accessed with the will-download event. The DownloadItem will not have any WebContents associated with it and the initial state will be interrupted. The download will start only when the resume API is called on the DownloadItem.

ses.clearAuthCache()

Returns Promise<void> - resolves when the session’s HTTP authentication cache has been cleared.

ses.setPreloads(preloads)

Adds scripts that will be executed on ALL web contents that are associated with this session just before normal preload scripts run.

ses.getPreloads()

Returns string[] an array of paths to preload scripts that have been registered.

ses.setCodeCachePath(path)

Sets the directory to store the generated JS code cache for this session. The directory is not required to be created by the user before this call, the runtime will create if it does not exist otherwise will use the existing directory. If directory cannot be created, then code cache will not be used and all operations related to code cache will fail silently inside the runtime. By default, the directory will be Code Cache under the respective user data folder.

ses.clearCodeCaches(options)

Returns Promise<void> - resolves when the code cache clear operation is complete.

ses.setSpellCheckerEnabled(enable)

Sets whether to enable the builtin spell checker.

ses.isSpellCheckerEnabled()

Returns boolean - Whether the builtin spell checker is enabled.

ses.setSpellCheckerLanguages(languages)

The built in spellchecker does not automatically detect what language a user is typing in. In order for the spell checker to correctly check their words you must call this API with an array of language codes. You can get the list of supported language codes with the ses.availableSpellCheckerLanguages property.

Note: On macOS the OS spellchecker is used and will detect your language automatically. This API is a no-op on macOS.

ses.getSpellCheckerLanguages()

Returns string[] - An array of language codes the spellchecker is enabled for. If this list is empty the spellchecker will fallback to using en-US. By default on launch if this setting is an empty list Electron will try to populate this setting with the current OS locale. This setting is persisted across restarts.

Note: On macOS the OS spellchecker is used and has its own list of languages. This API is a no-op on macOS.

ses.setSpellCheckerDictionaryDownloadURL(url)

By default Electron will download hunspell dictionaries from the Chromium CDN. If you want to override this behavior you can use this API to point the dictionary downloader at your own hosted version of the hunspell dictionaries. We publish a hunspell_dictionaries.zip file with each release which contains the files you need to host here.

The file server must be case insensitive. If you cannot do this, you must upload each file twice: once with the case it has in the ZIP file and once with the filename as all lowercase.

If the files present in hunspell_dictionaries.zip are available at https://example.com/dictionaries/language-code.bdic then you should call this api with ses.setSpellCheckerDictionaryDownloadURL('https://example.com/dictionaries/'). Please note the trailing slash. The URL to the dictionaries is formed as ${url}${filename}.

Note: On macOS the OS spellchecker is used and therefore we do not download any dictionary files. This API is a no-op on macOS.

ses.listWordsInSpellCheckerDictionary()

Returns Promise<string[]> - An array of all words in app’s custom dictionary. Resolves when the full dictionary is loaded from disk.

ses.addWordToSpellCheckerDictionary(word)

Returns boolean - Whether the word was successfully written to the custom dictionary. This API will not work on non-persistent (in-memory) sessions.

Note: On macOS and Windows 10 this word will be written to the OS custom dictionary as well

ses.removeWordFromSpellCheckerDictionary(word)

Returns boolean - Whether the word was successfully removed from the custom dictionary. This API will not work on non-persistent (in-memory) sessions.

Note: On macOS and Windows 10 this word will be removed from the OS custom dictionary as well

ses.loadExtension(path[, options])

Returns Promise<Extension> - resolves when the extension is loaded.

This method will raise an exception if the extension could not be loaded. If there are warnings when installing the extension (e.g. if the extension requests an API that Electron does not support) then they will be logged to the console.

Note that Electron does not support the full range of Chrome extensions APIs. See Supported Extensions APIs for more details on what is supported.

Note that in previous versions of Electron, extensions that were loaded would be remembered for future runs of the application. This is no longer the case: loadExtension must be called on every boot of your app if you want the extension to be loaded.

const { app, session } = require('electron')
const path = require('path')

app.on('ready', async () => {
  await session.defaultSession.loadExtension(
    path.join(__dirname, 'react-devtools'),
    // allowFileAccess is required to load the devtools extension on file:// URLs.
    { allowFileAccess: true }
  )
  // Note that in order to use the React DevTools extension, you'll need to
  // download and unzip a copy of the extension.
})

This API does not support loading packed (.crx) extensions.

Note: This API cannot be called before the ready event of the app module is emitted.

Note: Loading extensions into in-memory (non-persistent) sessions is not supported and will throw an error.

ses.removeExtension(extensionId)

Unloads an extension.

Note: This API cannot be called before the ready event of the app module is emitted.

ses.getExtension(extensionId)

Returns Extension null - The loaded extension with the given ID.

Note: This API cannot be called before the ready event of the app module is emitted.

ses.getAllExtensions()

Returns Extension[] - A list of all loaded extensions.

Note: This API cannot be called before the ready event of the app module is emitted.

ses.getStoragePath()

A string | null indicating the absolute file system path where data for this session is persisted on disk. For in memory sessions this returns null.

Instance Properties

The following properties are available on instances of Session:

ses.availableSpellCheckerLanguages Readonly

A string[] array which consists of all the known available spell checker languages. Providing a language code to the setSpellCheckerLanguages API that isn’t in this array will result in an error.

ses.spellCheckerEnabled

A boolean indicating whether builtin spell checker is enabled.

ses.storagePath Readonly

A string | null indicating the absolute file system path where data for this session is persisted on disk. For in memory sessions this returns null.

ses.cookies Readonly

A Cookies object for this session.

ses.serviceWorkers Readonly

A ServiceWorkers object for this session.

ses.webRequest Readonly

A WebRequest object for this session.

ses.protocol Readonly

A Protocol object for this session.

const { app, session } = require('electron')
const path = require('path')

app.whenReady().then(() => {
  const protocol = session.fromPartition('some-partition').protocol
  if (!protocol.registerFileProtocol('atom', (request, callback) => {
    const url = request.url.substr(7)
    callback({ path: path.normalize(`${__dirname}/${url}`) })
  })) {
    console.error('Failed to register protocol')
  }
})

ses.netLog Readonly

A NetLog object for this session.

const { app, session } = require('electron')

app.whenReady().then(async () => {
  const netLog = session.fromPartition('some-partition').netLog
  netLog.startLogging('/path/to/net-log')
  // After some network events
  const path = await netLog.stopLogging()
  console.log('Net-logs written to', path)
})
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