Written with a zero knowledge of Web3.js and one week's experience of Bootstrap....
start()
if (typeof web3 !== 'undefined')
web3 is set by Metamask - use that if it is available
otherwise
web3 = new Web3();
web3.setProvider(new web3.providers.HttpProvider('https://api.myetherapi.com/eth'));
create a new web3 object and link it up to MyEtherWallet' s API.
(if you are going to make a lot of calls please use infura instead)
getBalance()
Loads of ways we could do this but since I am a low level hacker, I found somebody's notes on how to do this from a low level call.
balanceOf(address) gets converted to the following data
keccak-256('balanceof(address)') => 0x70a08231
The address is encoded in 256 bits which means it needs to be padded with 24 zeros -
000000000000000000000000 followed by the address (with the 0x stripped off)
This gets sent in the data field to the GOLDX token contract at 0xeAb43193CF0623073Ca89DB9B712796356FA7414 with a value of zero via a call (not transaction) function.
convert the answer from Wei to Ether (i.e. to 18 decimal places) and we are done!