Metamask – How to Call Deployed Contract Functions

I have found a fix for my problem (and answer here for people who find this in the future) - in the Metamask window, even though I am deploying to Ropsten test network, it turns out that I need to set the network "tick" on localhost:8545 rather than on the Ropsten network directly - if I do this, then I get correct values returned.

Hope this helps someone...

You will need to create an HTML page that uses the web3 library to interact with your Ethereum-enabled browser (MetaMask, Mist, etc.).

First include web3.js or web3.min.js in your HTML, then you will be able to call JavaScript functions that interact with accounts and contracts, check syncing status and block numbers, etc.

<script src="web3.min.js"></script>

Here is an example of how to instantiate a web3 instance:

if (typeof web3 !== 'undefined') {
  web3 = new Web3(web3.currentProvider);
} else {
  // browser is not web3-enabled
}

Then you can use it like this:

web3.eth.getBlock(48, function(error, result){
    if(!error)
        console.log(result)
    else
        console.error(error);
})

Here is the API reference: https://github.com/ethereum/wiki/wiki/JavaScript-API

Heads up: The API reference has a lot of examples of synchronous calls, but web3 has deprecated them in a lot of cases. Most of the function calls will need to specify callbacks.