To fix the error, we can remove both of our error handlers from both the then calls, and replace them with a call at the very bottom, to a different method, which we'll call .catch:

asyncAdd(5, '7').then((res) => {
 console.log('Result:', res);
 return asyncAdd(res, 33);
}).then((res) => {
 console.log('Should be 45', res);
}).catch;

The catch promise method is similar to then, but it just takes one function. This is the error handler. As shown in the following code, we can specify one error handler if any of our promise calls fail. We'll take errorMessage and print it to the screen using console.log(errorMessage):

asyncAdd(5, '7').then((res) => {
 console.log('Result:', res);
 return asyncAdd(res, 33);
}).then((res) => {
 console.log('Should be 45', res);
}).catch((errorMessage) => {
 console.log(errorMessage)
});

For now though, if things are a little blurry that is okay, as long as you're starting to see exactly what we're doing. We're taking the result from one promise and passing it to a different one. In this case, the result works exactly as expected. The first promise fails, we get, Arguments must be numbers printing to the screen. Also, we don't get that broken statement where we try to print 45, but we get undefined instead. Using catch, we can specify an error handler that will fire for all of our previous failures. This is exactly what we want.