metamask-extension/app/scripts/controllers/network/enums.js

export const ROPSTEN = 'ropsten'
export const RINKEBY = 'rinkeby'
export const KOVAN = 'kovan'
export const MAINNET = 'mainnet'
export const LOCALHOST = 'localhost'
export const GOERLI = 'goerli'

export const MAINNET_CODE = 1
export const ROPSTEN_CODE = 3
export const RINKEBY_CODE = 4
export const KOVAN_CODE = 42
export const GOERLI_CODE = 5

export const ROPSTEN_DISPLAY_NAME = 'Ropsten'
export const RINKEBY_DISPLAY_NAME = 'Rinkeby'
export const KOVAN_DISPLAY_NAME = 'Kovan'
export const MAINNET_DISPLAY_NAME = 'Main Ethereum Network'
export const GOERLI_DISPLAY_NAME = 'Goerli'