A code snippet that checks which ethereum network your on.

currentNetwork.js

function currentNetwork() {
  const network = web3.eth.getBlock(0).hash
  const main = '0xd4e56740f876aef8c010b86a40d5f56745a118d0906a34e69aec8c0db1cb8fa3'
  const test = '0x41941023680923e0fe4d74a34bdac8141f2540e3ae90623718e47d66d1ca4a2d'

  switch (network) {
    case main:
      return 'Main Net'
    case test:
      return 'Ropsten Network'
    default:
      return 'TestRPC Testnet'
  }
}