protocol/packages/website/md/docs/0xjs/async.md

0x.js is a promise-based library. This means that whenever an asynchronous call is required, the library method will return a native Javascript promise. You can therefore choose between using promise or async/await syntax when calling our async methods.

Async/await syntax (recommended):

try {
    var availableAddresses = await zeroEx.getAvailableAddressesAsync();
} catch (error) {
    console.log('Caught error: ', error);
}

Promise syntax:

zeroEx
    .getAvailableAddressesAsync()
    .then(function(availableAddresses) {
        console.log(availableAddresses);
    })
    .catch(function(error) {
        console.log('Caught error: ', error);
    });

As is the convention with promise-based libraries, if an error occurs, it is thrown. It is the callers responsibility to catch thrown errors and to handle them appropriately.