Promises and async programming
JavaScript now has a new native pattern for writing asynchronous code called the Promise pattern. This new pattern removes the common code issues that the event and callback pattern had. It also makes the code look more like synchronous code. A promise (or a Promise object) represents an asynchronous operation. Existing asynchronous JavaScript APIs are usually wrapped with promises, and the new JavaScript APIs are purely implemented using promises. Promises are new in JavaScript but are already present in many other programming languages. Programming languages, such as C# 5, C++ 11, Swift, Scala, and more are some examples that support promises.
Let's see how to use promises.
Promise states
A promise is always in one of these states:
- Fulfilled: If the resolve callback is invoked with a non-promise object as the argument or no argument, then we say that the promise is fulfilled
- Rejected: If the rejecting callback is invoked or an exception occurs in the executor...
