Example #2 for "How to make a user friendly Ethereum dApp"

signTypedData.js

const user = web3.eth.accounts[0];

const sigInput = [
  { type: "string", name: "Action", value: "Create Account" },
  { type: "address", name: "Address", value: user           }
];

web3.currentProvider.sendAsync(
  { method: "eth_signTypedData", params: [sigInput, user], from: user },
  handleSignature
);