Call functions in contract returns promise error

Here is the code I used to call setValue and getValue in contract Hello.sol deployed with etherjs 5.0.14 on android/windows10:

 import { ContractFactory, ethers } from "ethers";

 let url = "http://localhost:8545";
 const provider = new ethers.providers.JsonRpcProvider(url);
 const signer = provider.getSigner(); //forJsonRPC

 let contract_at_address = new ethers.Contract(contract.address, abi, signer); //<<==contract.address is the deployed address. abi and signer were defined earlier.
 await contract_at_address.setValue(10); //<<setter
 let value = await contract_at_address.getValue(); //<<==value shall be 10
 console.log("value contract at address : ", value)

But it throws error:

[Sun Nov 15 2020 23:10:11.457]  WARN     Possible Unhandled Promise Rejection (id: 0):
Error: call revert exception (method="getValue()", errorSignature=null, errorArgs=[null], reason=null, code=CALL_EXCEPTION,   version=abi/5.0.5)
makeError@http://10.0.2.2:8081/index.bundle?platform=android&dev=true&minify=false:110810:32
throwError@http://10.0.2.2:8081/index.bundle?platform=android&dev=true&minify=false:110820:31
http://10.0.2.2:8081/index.bundle?platform=android&dev=true&minify=false:118492:68
step@http://10.0.2.2:8081/index.bundle?platform=android&dev=true&minify=false:118174:29
fulfilled@http://10.0.2.2:8081/index.bundle?platform=android&dev=true&minify=false:118058:34
tryCallOne@http://10.0.2.2:8081/index.bundle?platform=android&dev=true&minify=false:26991:16
http://10.0.2.2:8081/index.bundle?platform=android&dev=true&minify=false:27092:27
_callTimer@http://10.0.2.2:8081/index.bundle?platform=android&dev=true&minify=false:30531:17
_callImmediatesPass@http://10.0.2.2:8081/index.bundle?platform=android&dev=true&minify=false:30570:17
callImmediates@http://10.0.2.2:8081/index.bundle?platform=android&dev=true&minify=false:30787:33
__callImmediates@http://10.0.2.2:8081/index.bundle?platform=android&dev=true&minify=false:2736:35
http://10.0.2.2:8081/index.bundle?platform=android&dev=true&minify=false:2522:34
__guard@http://10.0.2.2:8081/index.bundle?platform=android&dev=true&minify=false:2719:15
flushedQueue@http://10.0.2.2:8081/index.bundle?platform=android&dev=true&minify=false:2521:21
flushedQueue@[native code]
invokeCallbackAndReturnFlushedQueue@[native code]

Here is the Hello.sol:

pragma solidity 0.7.0;

contract Hello {
   address owner;
   uint256 value;

   event initContract(address _owner);
   constructor() {
      owner = msg.sender;
      emit initContract(owner);
   }

   function setValue(uint256 _value) public {
       value = _value;
  }
 
   function getValue() view public returns (uint256) {
      return value;
  }

}

I am following the doc for contract. The same functions are tested in truffle/ganache and they all work fine. What’s missing here to call setValue (change state) and getValue (view only) functions in ethersjs?

[ricmoo]

Exactly what @zemse mentioned.

Also, in a real application, you won’t write a value to a contract and immediately read it. You would set up event listeners and let the events from you or other users trigger that.

You only need to await here because you are attempting consistent writes and reads.

A full application will have more complex interactions, but will be largely asynchronous. 😃

[zemse]

You are correct that for most users, the UX waiting for tx to be confirmed is annoying. You can have a look at Uniswap’s UX how they handle this case. They push the transaction hash to a global array or transaction hashes. There user can click on a dropdown to see confirmation status and can do some more hacks with the transaction (like increasing gas price or so). This allows user to do other tasks in the dapp while tx is being confirmed in the background.