signature.js

const ethers  = require('ethers');

class Signature {
    constructor(ethereum) {
        this.ethereum = ethereum;
    }

    provider() {
		    return new ethers.providers.Web3Provider(this.ethereum);
	  }

	  signer() {
		    return this.provider().getSigner();
	  }

	  async sign(message) {
		    const wallet = await this.signer();
		    const address = await wallet.getAddress();
		    const signature = await wallet.signMessage(message + ':' + address);
	  }
}

window.Signature = Signature;