JavaScript Promise constructor Last Updated : 08 Aug, 2023 Comments Improve Suggest changes Like Article Like Report JavaScript Promises are used to handle asynchronous operations in JavaScript. They are easy to manage when dealing with multiple asynchronous operations where callbacks can create callback hell leading to unmanageable code. Promise constructor in JavaScript is mainly used to wrap functions that do not already support promises. Syntax: new Promise(executor)Parameters: The promise constructor contains a single parameter: executor: The executor can be the custom code that ties an outcome to a promise. You, the programmer, write the executor. Return Value: Another promise object, in which case the promise gets dynamically inserted into the chain. Example 1: Creating only one promise constructor. JavaScript // Creating an new promise and resolving geeks for geeks const promise1 = new Promise((resolve, reject) => { setTimeout(() => { resolve('geeks for geeks'); }, 100); }); promise1.then((value) => { console.log(value); // output will be : geeks for geeks }); // output will be : [object Promise] console.log(promise1); OutputPromise { <pending> } geeks for geeks Example 2: In this code, we are going to create two promise constructors. JavaScript // Creating first promise constructor const promise1 = new Promise((resolve, reject) => { setTimeout(() => { resolve('geeks for geeks'); }, 100); }); ////creating second promise constructor const promise2 = new Promise((resolve, reject) => { setTimeout(() => { resolve('computer science portal'); }, 100); }); promise2.then((value) => { console.log(value); // output: "computer science portal" }); promise1.then((value) => { console.log(value); // output: "geeks for geeks" }); console.log(promise1); // output: [object Promise] OutputPromise { <pending> } geeks for geeks computer science portalExample 3: In this example, we will display a value. JavaScript // Creating first promise constructor const promise1 = new Promise((resolve, reject) => { setTimeout(() => { resolve('geeks for geeks'); }, 100); }); // Creating second promise constructor const promise2 = new Promise((resolve, reject) => { setTimeout(() => { resolve('computer science portal'); }, 100); }); promise2.then((value) => { console.log(value); // output: "computer science portal" }); promise1.then((value) => { console.log(value); // output: "geeks for geeks" }); console.log(2 + 3); // output: [object Promise] Output5 geeks for geeks computer science portal Comment More infoAdvertise with us Next Article JavaScript Promise constructor Property S sravankumar_171fa07058 Follow Improve Article Tags : JavaScript Web Technologies javascript-functions Similar Reads JavaScript Promise constructor JavaScript Promises are used to handle asynchronous operations in JavaScript. They are easy to manage when dealing with multiple asynchronous operations where callbacks can create callback hell leading to unmanageable code. Promise constructor in JavaScript is mainly used to wrap functions that do n 2 min read JavaScript Promise constructor Property JavaScript Promise constructor property is used to return the Promise constructor function for the object. The function which is returned by this property is just a reference to this function, not a Promise containing the function's name. The JavaScript number constructor, string constructor, and bo 1 min read JavaScript Promise all() Method The Promise.all() method in JavaScript is used for handling multiple asynchronous operations simultaneously. It takes an array (or any iterable) of promises and returns a single promise that resolves when all the input promises resolve or reject if any one of the promises fails. This makes it ideal 6 min read JavaScript Promise allSettled() Method Promise.allSettled() method in JavaScript is used to handle multiple promises concurrently and return a single promise. This promise is fulfilled with an array of promise state descriptors, each describing the outcome of the corresponding promise in the input array. Unlike Promise.all(), Promise.all 2 min read JavaScript Promise race() Method The Promise.race() method returns a promise that fulfills or rejects as soon as one of the promises in an iterable fulfills or rejects, with the value or reason from that promise. We may think of this particular method as in the form of a real-life example where several people are running in a race 2 min read JavaScript promise reject() Method The Promise.reject() method is used to return a rejected Promise object with a given reason for rejection. It is used for debugging purposes and selective error-catching. The catch() method can be used for logging the output of the reject() method to the console that is catch() method acts as a care 3 min read JavaScript promise resolve() Method The Promise.resolve() method in JavaScript returns a Promise object that is resolved with a given value. If the value is a promise, it returns that promise; otherwise, it resolves the value as a new promise, making it useful for simplifying asynchronous code handling.What is Promise resolve() method 3 min read JavaScript Promise catch() Method JavaScript Promise catch() method is called whenever a promise is rejected. This method itself returns a promise so it can also be used to chain promises. This method is used for error handling. This method is mainly used after .then to chain a promise and handle reject condition. This method intern 2 min read JavaScript Promise then() Method JavaScript Promise then() method is called whenever a promise is resolved. It takes data from the resolved promise. It can take up to two arguments which are callback functions for the fulfilled and rejected cases respectively. Just like the catch() method it also returns a Promise so it is used to 2 min read JavaScript Promise finally() Method The finally() method of the Promise object is used to return a callback when a Promise is settled (either fulfilled or rejected).Syntax:task.finally(onFinally() { });Parameters: This method has a single parameter as mentioned above and described below:onFinally: It is the function that will be calle 1 min read Like