add toggle approved helper function

app/components/ens/registerSubDomain.js

@@ -1,5 +1,6 @@
 import web3 from "Embark/web3"
 import ENSSubdomainRegistry from 'Embark/contracts/ENSSubdomainRegistry';
+import TestToken from 'Embark/contracts/TestToken';
 import React from 'react';
 import { connect } from 'react-redux';
 import Hidden from '@material-ui/core/Hidden';

app/utils/web3Helpers.js

@@ -1,3 +1,17 @@
 import web3 from "Embark/web3"
+import BigNumber from 'bignumber.js';
 
+// By default BigNumber's `toString` method converts to exponential notation if the value has
+// more then 20 digits. We want to avoid this behavior, so we set EXPONENTIAL_AT to a high number
+BigNumber.config({
+  EXPONENTIAL_AT: 1000,
+});
+const unlimitedAllowance = new BigNumber(2).pow(256).sub(1);
 export const getDefaultAccount = () => web3.eth.defaultAccount;
+export const toggleApproved = (token, spender, approved, onlyApprove = false) => {
+  const isApproved = !!Number(approved);
+  if (isApproved && onlyApprove) return;
+  const { approve } = token.methods;
+  const amountToApprove = isApproved ? 0 : unlimitedAllowance;
+  return approve(spender,amountToApprove).send();
+}