When it comes to JavaScript, a promise that is fulfilled is said to be resolved while that that is broken is said to be rejected. Das mit ECMAScript 2015 (ES6) eingeführte Konstruktorfunktion Promise dient dazu, asynchrone Abläufe zu steuern und zu koordinieren. ES6 came with many new features, but one of the best features was the official introduction of Promises. We’ll see that in the next chapters. That’s all right, as our task is usually to perform “general” finalizing procedures. And trust me, you are not alone! Multiple callbacks may be added by calling .then several times, to be executed independently in insertion order. Instead, it will create and return a Promise object that resolves when the loading is complete. Many functions may need that result. Today’s video will cover what are promise in JavaScript and a bit about the different states of Promises. Like throw in plain old JavaScript, it's customary, but not required, to reject with an Error object. To demonstrate the use of promises, we will use the callback examples from the previous chapter: ECMAScript 2015, also known as ES6, introduced the JavaScript Promise object. For instance, here’s a reaction to a successfully resolved promise: And in the case of a rejection, the second one: If we’re interested only in successful completions, then we can provide only one function argument to .then: If we’re interested only in errors, then we can use null as the first argument: .then(null, errorHandlingFunction). 3. The second argument of .then is a function that runs when the promise is rejected, and receives the error. So what are promises? The executor should call only one resolve or one reject. The promise is one of the easiest ways to achieve the asynchronous process in Javascript. Just like there’s a finally clause in a regular try {...} catch {...}, there’s finally in promises. When a Promise object is "fulfilled", the result is a value. A promise that is either resolved or rejected is called “settled”, as opposed to an initially “pending” promise. A promise is an object that will return a resolved object or reject an object sometime in the future. All further calls of resolve and reject are ignored: The idea is that a job done by the executor may have only one result or an error. You cannot access the Promise properties state and result. Imagine that you’re a top singer, and fans ask day and night for your upcoming single. The promise in JavaScript is used to represent any operation that is deferred or is expected to be completed in the future, as an asynchronous ajax request. A Promise has two parts 1) Promise creation and 2) consuming a Promise. A Promise object represents a value that may not be available yet, but will be resolved at some point in the future. Our code is only inside the executor. For example, if you use the promise API to make an asynchronous call to a remote web service, you will create a Promise object which represents the data that will be returned by the web service in future. In JavaScript, a promise is an object that represents an asynchronous operation. That promise should resolve after ms milliseconds, so that we can add .then to it, like this: Please note that in this task resolve is called without arguments. Consuming functions can be registered (subscribed) using methods .then, .catch and .finally. The Promise object has three types: Pending, Resolve, and Reject. Let's see Promise.then() method, the 2nd argument of Promise.then() can be set to a Func to receive the result of rejection when receiving the result of then.. Syntax Usage Promise.then(onFulfilled[, onRejected]);. In finally we don’t know whether the promise is successful or not. 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