jQuery in Action, Third Edition

Chapter 13. Avoiding the callback hell with Deferred

This chapter covers

• What promises are and why they’re important
• The Deferred object
• How to manage multiple asynchronous operations
• Resolving and rejecting a promise

For a long time, JavaScript developers have used callback functions to perform several tasks such as running operations after a given amount of time (using set-Timeout()), or at regular intervals (using setInterval()), or to react to a given event (click, keypress, load, and so on). We’ve discussed and employed callbacks extensively to perform asynchronous operations; for example, in chapter 6 where we focused on events, in chapter 8 when we talked about animations, and in chapter 10 where we covered Ajax. Callback functions ...