Continuation Pasing Style (CPS)

• passes handler as callback argument
• by convention first argument of callback is for errors

function callback(error, data) {
  if (error) {
    // handle error
  }
  // handle data
}

asyncOperation(..., callback);

Problems

• misuses callback as control flow, conflates input and output, gives input to handle output
• subsequential async calls are nested, “callback hell”
• no guarantees how callback is called, e.g. if called, how often called, with what arguments called, if called synchronously or asynchronously, etc.
• can’t return, because would yield back into API
• can’t throw errors, because would yield back into API
• needs to handle errors, can’t ignore, not automatically passed up the call stack until someone handles it
• looses call stack