Challenges with using async await alongside synchronous functions

Question

Challenges with using async await alongside synchronous functions

I'm currently navigating through a library that utilizes async functions and feeling a bit overwhelmed. I'm attempting to call a function that should return a string, but I'm hitting some roadblocks. As I understand it, the ZeroEx library functions all require async/await, meaning I can only call them from another async method. Does this imply that every method in my code needs to be async as well? Or am I missing something crucial?

function main() {
    var broker = zmq.socket('router');
    broker.bindSync('tcp://*:5671');


    broker.on('message', function () {
    var args = Array.apply(null, arguments)
        , identity = args[0]
        , message = args[1].toString('utf8');

        if(message === 'TopOfBook') {
            broker.send([identity, '', getTopOfBook()]);
        }

        //broker.send([identity, '', 'TEST']);
        //console.log('test sent');
    })
}

async function getTopOfBook() {
    var result: string = 'test getTopOfBook';
    const EXCHANGE_ADDRESS = await zeroEx.exchange.getContractAddress();
    const wethTokenInfo = await zeroEx.tokenRegistry.getTokenBySymbolIfExistsAsync('WETH');
    const zrxTokenInfo = await zeroEx.tokenRegistry.getTokenBySymbolIfExistsAsync('ZRX');

    if (wethTokenInfo === undefined || zrxTokenInfo === undefined) {
        throw new Error('could not find token info');
    }

    const WETH_ADDRESS = wethTokenInfo.address;
    const ZRX_ADDRESS = zrxTokenInfo.address;


    return result;
}

main();

The getTopOfBook() function isn't returning any value to the main() function, causing the result to never get sent by the broker. However, the commented out broker.send() with 'TEST' is functioning properly. Thank you for your assistance.

EDIT: I tried to make the main method async to incorporate await, but encountered an error stating that I can only use await in an async function. Could it be the broker.on() call causing this issue?

  const main = async () => {
      try{
      var broker = zmq.socket('router');
      broker.bindSync('tcp://*:5671');


      broker.on('message', function () {
      var args = Array.apply(null, arguments)
          , identity = args[0]
          , message = args[1].toString('utf8');

          console.log(message);
          if(message === 'TopOfBook') {
>>            var test = await getTopOfBook();
              console.log('in top of book test');

              broker.send([identity, '', test]);
          }

          //broker.send([identity, '', 'TEST']);
          //console.log('test sent');
      })
      } catch (err) {
          console.log(err);
      }
  }

EDIT 2: Here's my current working code. A big thank you to everyone who provided advice/solutions! I still need to complete the getTopOfBook() function to actually return a result. If you have more suggestions, please feel free to share them. I'm working on setting up a backend that fetches data from a geth rpc and sends it to a C# GUI front end.

var main = function() {
    try{
    var broker = zmq.socket('router');
    broker.bindSync('tcp://*:5672');

    broker.on('message', function () {
    var args = Array.apply(null, arguments)
        , identity = args[0]
        , message = args[1].toString('utf8');

        if(message === 'TopOfBook') {
            getTopOfBook().then((result) => {
                broker.send([identity, '', result])
            });
        }
    })
    } catch (err) {
        console.log(err);
    }
}

async function getTopOfBook() {
    var result: string = 'test getTopOfBook';
    const EXCHANGE_ADDRESS = await zeroEx.exchange.getContractAddress();
    const wethTokenInfo = await zeroEx.tokenRegistry.getTokenBySymbolIfExistsAsync('WETH');
    const zrxTokenInfo = await zeroEx.tokenRegistry.getTokenBySymbolIfExistsAsync('ZRX');

    if (wethTokenInfo === undefined || zrxTokenInfo === undefined) {
        throw new Error('could not find token info');
    }

    const WETH_ADDRESS = wethTokenInfo.address;
    const ZRX_ADDRESS = zrxTokenInfo.address;


    return result;
}

main();

javascript typescript asynchronous async-await

Answer 1

Answer №1

It is important that the callback function is marked as asynchronous

broker.on('message', async function () {
    var args = Array.apply(null, arguments)
        , identity = args[0]
        , message = args[1].toString('utf8');

        if(message === 'TopOfBook') {
            var result = await fetchTopOfBookData();
            broker.send([identity, '', result]);
        }

        //broker.send([identity, '', 'TEST']);
        //console.log('Data sent successfully');
    })

Answer 2

It is important that the callback function is marked as asynchronous

broker.on('message', async function () {
    var args = Array.apply(null, arguments)
        , identity = args[0]
        , message = args[1].toString('utf8');

        if(message === 'TopOfBook') {
            var result = await fetchTopOfBookData();
            broker.send([identity, '', result]);
        }

        //broker.send([identity, '', 'TEST']);
        //console.log('Data sent successfully');
    })

Answer 3

Answer №2

It's important to understand that async functions are simply a way to write code. Under the hood, every async function actually generates a promise. This allows you to use the await keyword with any promise and seamlessly interact with libraries that utilize async functionality without needing to write async functions yourself.

When you invoke an async function, it will automatically return a promise. A promise is essentially an object with a then method, which accepts a callback to handle the resulting logic.

function main() {
    var broker = zmq.socket('router');
    broker.bindSync('tcp://*:5671');

    broker.on('message', function () {
        var args = Array.apply(null, arguments)
            , identity = args[0]
            , message = args[1].toString('utf8');

        if(message === 'TopOfBook') {
            return getTopOfBook().then(result => 
                broker.send([identity, '', result])
            ) // If the broker also returns a promise, you can continue the flow here
            .then(() => console.log('test sent'))
        }
    })
}

Personally, I'm not a fan of async/await because they can obscure the underlying nature of promises and asynchronous code.

When working with promises, always remember to return any promises you create or call so that the outer code can seamlessly continue the chain and handle any error messages.

Answer 4

It's important to understand that async functions are simply a way to write code. Under the hood, every async function actually generates a promise. This allows you to use the await keyword with any promise and seamlessly interact with libraries that utilize async functionality without needing to write async functions yourself.

When you invoke an async function, it will automatically return a promise. A promise is essentially an object with a then method, which accepts a callback to handle the resulting logic.

function main() {
    var broker = zmq.socket('router');
    broker.bindSync('tcp://*:5671');

    broker.on('message', function () {
        var args = Array.apply(null, arguments)
            , identity = args[0]
            , message = args[1].toString('utf8');

        if(message === 'TopOfBook') {
            return getTopOfBook().then(result => 
                broker.send([identity, '', result])
            ) // If the broker also returns a promise, you can continue the flow here
            .then(() => console.log('test sent'))
        }
    })
}

Personally, I'm not a fan of async/await because they can obscure the underlying nature of promises and asynchronous code.

When working with promises, always remember to return any promises you create or call so that the outer code can seamlessly continue the chain and handle any error messages.

Answer 5

Answer №3

Your function getTopOfBook is designed to return a Promise, which means you should utilize the then function to handle the asynchronous response.

To call this function, use the following syntax:

getTopOfBook().then((result) => {
  console.log("Result:" + result);
});

Take a Closer Look at this Code Snippet

let sleep = (fn) => {
  setTimeout(fn, 1000);
};

let getContractAddress = function(cb) {
  return new Promise((r) => sleep(() => {
    r('getContractAddress')
  }));
};

let getTokenBySymbolIfExistsAsync = function(str) {
  return new Promise((r) => sleep(() => {
    r({
      address: 'getTokenBySymbolIfExistsAsync: ' + str
    })
  }));
};

let WETH_ADDRESS = '';
let ZRX_ADDRESS = '';
let EXCHANGE_ADDRESS = '';

async function getTopOfBook() {
  var result = 'test getTopOfBook';

  const EXCHANGE_ADDRESS = await getContractAddress();
  const wethTokenInfo = await getTokenBySymbolIfExistsAsync('WETH');
  const zrxTokenInfo = await getTokenBySymbolIfExistsAsync('ZRX');

  if (wethTokenInfo === undefined || zrxTokenInfo === undefined) {
    return Promise.reject(new Error('could not find token info'));
  }

  const WETH_ADDRESS = wethTokenInfo.address;
  const ZRX_ADDRESS = zrxTokenInfo.address;

  console.log(WETH_ADDRESS);
  console.log(ZRX_ADDRESS);
  console.log(EXCHANGE_ADDRESS);

  return result;
}

var main = function() {
  console.log('Waiting response...');
  getTopOfBook().then((result) => {
    console.log("Result:" + result);
    console.log('DONE!');
  }).catch((error) => {
      console.log(error);
  });      
};

main();

.as-console-wrapper {
  max-height: 100% !important
}

If you encounter an error, you can handle it by utilizing the Promise.reject() function.

When calling the function, you should either pass the reject function or invoke the catch function to handle any errors.

In this example, we're demonstrating passing the reject function:

(error) => {
    console.log(error); 
}

If you don't pass the reject function, you'll need to use the catch function to manage any thrown errors.

let sleep = (fn) => {
  setTimeout(fn, 1000);
};

let getContractAddress = function(cb) {
  return new Promise((r) => sleep(() => {
    r('getContractAddress')
  }));
};

let getTokenBySymbolIfExistsAsync = function(str) {
  return new Promise((r) => sleep(() => {
    r()
  }));
};

let WETH_ADDRESS = '';
let ZRX_ADDRESS = '';
let EXCHANGE_ADDRESS = '';

async function getTopOfBook() {
  var result = 'test getTopOfBook';

  const EXCHANGE_ADDRESS = await getContractAddress();
  const wethTokenInfo = await getTokenBySymbolIfExistsAsync('WETH');
  const zrxTokenInfo = await getTokenBySymbolIfExistsAsync('ZRX');

  if (wethTokenInfo === undefined || zrxTokenInfo === undefined) {
    return Promise.reject('Could not find token info');
  }

  const WETH_ADDRESS = wethTokenInfo.address;
  const ZRX_ADDRESS = zrxTokenInfo.address;

  console.log(WETH_ADDRESS);
  console.log(ZRX_ADDRESS);
  console.log(EXCHANGE_ADDRESS);

  return result;
}

var main = function() {
  console.log('Waiting response...');
  getTopOfBook().then((result) => {
    console.log("Result:" + result);
    console.log('DONE!');
  }, (error) => {
    console.log(error); 
  }).catch((error) => {
    console.log(error); // This line will be called if reject function is missing.
  });

};

main();

.as-console-wrapper {
  max-height: 100% !important
}

Additional Resources

When invoking an async function, a Promise is returned. If the async function successfully resolves, the Promise will be resolved with the returned value. If the function encounters an exception, the Promise will be rejected with the thrown value.

Answer 6

Your function getTopOfBook is designed to return a Promise, which means you should utilize the then function to handle the asynchronous response.

To call this function, use the following syntax:

getTopOfBook().then((result) => {
  console.log("Result:" + result);
});

Take a Closer Look at this Code Snippet

let sleep = (fn) => {
  setTimeout(fn, 1000);
};

let getContractAddress = function(cb) {
  return new Promise((r) => sleep(() => {
    r('getContractAddress')
  }));
};

let getTokenBySymbolIfExistsAsync = function(str) {
  return new Promise((r) => sleep(() => {
    r({
      address: 'getTokenBySymbolIfExistsAsync: ' + str
    })
  }));
};

let WETH_ADDRESS = '';
let ZRX_ADDRESS = '';
let EXCHANGE_ADDRESS = '';

async function getTopOfBook() {
  var result = 'test getTopOfBook';

  const EXCHANGE_ADDRESS = await getContractAddress();
  const wethTokenInfo = await getTokenBySymbolIfExistsAsync('WETH');
  const zrxTokenInfo = await getTokenBySymbolIfExistsAsync('ZRX');

  if (wethTokenInfo === undefined || zrxTokenInfo === undefined) {
    return Promise.reject(new Error('could not find token info'));
  }

  const WETH_ADDRESS = wethTokenInfo.address;
  const ZRX_ADDRESS = zrxTokenInfo.address;

  console.log(WETH_ADDRESS);
  console.log(ZRX_ADDRESS);
  console.log(EXCHANGE_ADDRESS);

  return result;
}

var main = function() {
  console.log('Waiting response...');
  getTopOfBook().then((result) => {
    console.log("Result:" + result);
    console.log('DONE!');
  }).catch((error) => {
      console.log(error);
  });      
};

main();

.as-console-wrapper {
  max-height: 100% !important
}

If you encounter an error, you can handle it by utilizing the Promise.reject() function.

When calling the function, you should either pass the reject function or invoke the catch function to handle any errors.

In this example, we're demonstrating passing the reject function:

(error) => {
    console.log(error); 
}

If you don't pass the reject function, you'll need to use the catch function to manage any thrown errors.

let sleep = (fn) => {
  setTimeout(fn, 1000);
};

let getContractAddress = function(cb) {
  return new Promise((r) => sleep(() => {
    r('getContractAddress')
  }));
};

let getTokenBySymbolIfExistsAsync = function(str) {
  return new Promise((r) => sleep(() => {
    r()
  }));
};

let WETH_ADDRESS = '';
let ZRX_ADDRESS = '';
let EXCHANGE_ADDRESS = '';

async function getTopOfBook() {
  var result = 'test getTopOfBook';

  const EXCHANGE_ADDRESS = await getContractAddress();
  const wethTokenInfo = await getTokenBySymbolIfExistsAsync('WETH');
  const zrxTokenInfo = await getTokenBySymbolIfExistsAsync('ZRX');

  if (wethTokenInfo === undefined || zrxTokenInfo === undefined) {
    return Promise.reject('Could not find token info');
  }

  const WETH_ADDRESS = wethTokenInfo.address;
  const ZRX_ADDRESS = zrxTokenInfo.address;

  console.log(WETH_ADDRESS);
  console.log(ZRX_ADDRESS);
  console.log(EXCHANGE_ADDRESS);

  return result;
}

var main = function() {
  console.log('Waiting response...');
  getTopOfBook().then((result) => {
    console.log("Result:" + result);
    console.log('DONE!');
  }, (error) => {
    console.log(error); 
  }).catch((error) => {
    console.log(error); // This line will be called if reject function is missing.
  });

};

main();

.as-console-wrapper {
  max-height: 100% !important
}

Additional Resources

When invoking an async function, a Promise is returned. If the async function successfully resolves, the Promise will be resolved with the returned value. If the function encounters an exception, the Promise will be rejected with the thrown value.

Challenges with using async await alongside synchronous functions

Answer №1

Answer №2

Answer №3

Take a Closer Look at this Code Snippet

Additional Resources

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