[Ethereum] How to test if a TransactionHash is valid using web3

After adding an event like SquareComputed (see How to get values returned by non constant transaction functions?) and web3.js Contract Events example

var event = myContractInstance.MyEvent({valueA: 23} [, additionalFilterObject])

// watch for changes
event.watch(function(error, result){
  if (!error)
    console.log(result);
});

this would lead to code like:

var event = myContractInstance.SquareComputed({});

// watch for changes
event.watch(function(error, result){
  if (!error)
    resolve({
        primary_address: config.ethConfig.primary_address,
        numSquare : result  // need to access the properties of result to obtain the actual square 
    })
  event.stopWatching();
});

Do the above before myContractInstance.squareNumber.sendTransaction. The resolve({numSquare:...}) in the original code should be moved to inside the watch as above.

Other web3.js APIs such as web3.eth.filter can also be used (see How do I retrieve the Voted events from The DAO).

This questions asks "how exactly do I structure my web3js code, to get the value returned (10*10) from the solidity function squareNumber()", otherwise for an overview see What is the difference between a transaction and a call?.

The answer is

status: false

This indicates what you see on etherscan. If you try getting this field through web3, the response is usually 0x0 or 0x1.

So here you go:

web3.eth.getTransactionReceipt(txID, function (e, data) {
            if (e !== null) {
                console.log("Could not find a transaction for your id! ID you provided was " + txID);
            } else {
                console.log(data);
                if(data.status == '0x0') {
                    console.log("The contract execution was not successful, check your transaction !");
                } else {
                    console.log("Execution worked fine!");
                }