How to catch JSON RPC exception in front end web3

Question

I have a transaction in contract which "requires" only owner can call. In front end when I call this with accounts other than owner of the contract I want to display an error. Code below doesn't work. It says

:Uncaught (in promise) Error: Invalid JSON RPC response: {"id":6,"jsonrpc":"2.0"}

      this.state.web3.eth.getAccounts((error, accounts) => {
        TalioInterview.deployed().then((instance) => {
          try {
            return instance.isTalioOwner.call({from:accounts[1]})

          }catch(err){
            alert("You are not authorized to run this.");
          }

My contract looks as below

 function isTalioOwner()
    public onlyIfTalioOwner()
    constant
    returns(bool)
    {
        return true;
    }

Found a similar question here, but without any answer. What is the best solution here other than changing contract to return false for non-owner accounts ?

Answer 1

I'm not too familiar with Truffle. (I assume this is Truffle, right?) But just based on how Promises usually work, I think you want something like this:

instance.isTalioOwner.call({from:accounts[1]}).then((result) => {
  console.log("Success! Got result: " + result);
}).catch((err) => {
  console.log("Failed with error: " + err);
});

Answer 2

Truffle console will support internally web3js, with and without promises also. When you use call then, it will become async call. So it will look for callback/promise method.

 this.state.web3.eth.getAccounts((error, accounts) => {
    TalioInterview.deployed().then((instance) => {
       try{
            var result= instance.isTalioOwner({from:accounts[1]})
          }catch(e){
             console.log("error",e);
          }

     }));

Web3js will work, but people will recommend to use async method, because you no need to wait for next instruction to be execute. When your writing test cases you can use above method when it required, that will reduce pyramid code.

Find below screen shot for ref: