metamask-extension/app/scripts/lib/enums.js

const ENVIRONMENT_TYPE_POPUP = 'popup'
const ENVIRONMENT_TYPE_NOTIFICATION = 'notification'
const ENVIRONMENT_TYPE_FULLSCREEN = 'fullscreen'
const ENVIRONMENT_TYPE_BACKGROUND = 'background'

const PLATFORM_BRAVE = 'Brave'
const PLATFORM_CHROME = 'Chrome'
const PLATFORM_EDGE = 'Edge'
const PLATFORM_FIREFOX = 'Firefox'
const PLATFORM_OPERA = 'Opera'

const MAINNET_CHAIN_ID = '0x1'
const ROPSTEN_CHAIN_ID = '0x3'
const RINKEBY_CHAIN_ID = '0x4'
const KOVAN_CHAIN_ID = '0x2a'
const GOERLI_CHAIN_ID = '0x5'

export {
  ENVIRONMENT_TYPE_POPUP,
  ENVIRONMENT_TYPE_NOTIFICATION,
  ENVIRONMENT_TYPE_FULLSCREEN,
  ENVIRONMENT_TYPE_BACKGROUND,
  PLATFORM_BRAVE,
  PLATFORM_CHROME,
  PLATFORM_EDGE,
  PLATFORM_FIREFOX,
  PLATFORM_OPERA,
  MAINNET_CHAIN_ID,
  ROPSTEN_CHAIN_ID,
  RINKEBY_CHAIN_ID,
  KOVAN_CHAIN_ID,
  GOERLI_CHAIN_ID,
}