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1. Top results related to promise javascript

   • Javascript promise wait for AccessToken value

     Top Answer

     Answered Jul 26, 2016 · 0 votes

     Make your function getAccessToken to return a promise

     componentDidMount: function () { var component = this; getAccessToken() .then(function(accessToken) { var url = window.APIUrl +'services/?access_token=' + accessToken, return $.getJSON(url) }) .then(function(response) { component.setState({ services: response }); });}function getAccessToken(){ if(window.accessToken) { return $.when(window.accessToken) } return $.ajax(...) // get access token from server}

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     1/5

   • JavaScript Promise

     JavaScript Promises are used to simplify managing multiple asynchronous operations, preventing callback hell and unmanageable code. They represent future values, associating handlers with eventual success or failure, resembling synchronous methods by postponing value delivery.

     Syntax:

     let promise = new Promise(function(resolve, reject){ //do something});

     Parameters

     • The promise constructor takes only one argument which is a callback function
     • The callback function takes two arguments, resolve and reject
     • Perform operations inside the callback function and if everything went well then call resolve.
     • If desired operations do not go well then call reject.

     A Promise has four states

     StateDescriptionFulfilledAction related to the promise succeededRejectedAction related to the promise failedPendingPromise is still pending i.e. not fulfilled or rejected yetSettledPromise has been fulfilled or rejectedExample 1: In this example we create a promise comparing two strings. If they match, resolve; otherwise, reject. Then, log success or error accordingly. Simplifies asynchronous handling in JavaScript.

     -let promise = new Promise(function (resolve, reject) { const x = "geeksforgeeks"; const y = "geeksforgeeks" if (x === y) { resolve(); } else { reject(); }});promise. then(function () { console.log('Success, You are a GEEK'); }). catch(function () { console.log('Some error has occurred'); });

     Promise Consumers: Promises can be consumed by registering functions using .then and .catch methods.

     1. Promise then() MethodPromise method is invoked when a promise is either resolved or rejected. It may also be defined as a carrier that takes data from promise and further executes...

     • The first function is executed if the promise is resolved and a result is received.
     • The second function is executed if the promise is rejected and an error is received. (It is optional and there is a better way to handle error using .catch() method
     • Function to handle errors or promise rejections.(.catch() method internally calls .then(null, errorHandler), i.e. .catch() is just a shorthand for .then(null, errorHandler) )
     • Google Chrome 5.0
     • Edge 12
     • Mozilla 4.0
     • Safari 5.0
     • Opera 11.1

     Check all answers on Geeksforgeeks

     2/5

   • JavaScript Promise then() ordering

     Top Answer

     Answered Mar 17, 2015 · 35 votes

     The reason you see 6 early is because you didn't chain, you branched.

     When you call p.then().then().then(), you've got a chain of promises that must execute in the correct order. However, if you call p.then().then(); p.then(), you've got 2 promises attached to p - essentially creating a branch, and the 2nd branch will execute along with the first.

     You can fix this by ensuring you chain them together p = p.then().then(); p.then();

     FYI, you almost NEVER want to branch, unless you bring them back together (eg. Promise.all), or are intentionally creating a "fire and forget" branch.

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     3/5

   • Javascript Promise Exception Handling

     Top Answer

     Answered Nov 23, 2016 · 0 votes

     An Error in a Promise or in a .then will propagate down the Promise chain until it meets the first handler, which can be one of these two:

     .then(function(){}, function(err){}) // second callback is the handler.catch(function(err){})-

     where the .catch option is actually just syntactic sugar for:

     .then(null, function(err){}) -

     In your code the .then does not contain a handler and so the Error in api propagates to .catch.

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     4/5

   • Also try

     promise javascript w3schools	object promise javascript
     return promise javascript	asynchronous promise javascript
     resolve promise javascript	pending promise javascript
     how to create a promise javascript	await new promise javascript

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2. developer.mozilla.org › en-US › docsPromise - JavaScript | MDN - MDN Web Docs

   developer.mozilla.org › en-US › docs

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   Jul 30, 2024 · Description. A Promise is a proxy for a value not necessarily known when the promise is created. It allows you to associate handlers with an asynchronous action's eventual success value or failure reason.

3. www.w3schools.com › Js › js_promiseJavaScript Promises - W3Schools

   www.w3schools.com › Js › js_promise

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   Here is how to use a Promise: myPromise.then(. function(value) { /* code if successful */ }, function(error) { /* code if some error */ } ); Promise.then () takes two arguments, a callback for success and another for failure. Both are optional, so you can add a callback for success or failure only.

4. developer.mozilla.org › en-US › docsUsing promises - JavaScript | MDN - MDN Web Docs

   developer.mozilla.org › en-US › docs

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   Jul 26, 2024 · A Promise is an object representing the eventual completion or failure of an asynchronous operation. Since most people are consumers of already-created promises, this guide will explain consumption of returned promises before explaining how to create them.

5. javascript.info › promise-basicsPromise - The Modern JavaScript Tutorial

   javascript.info › promise-basics

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   A promise is a special JavaScript object that links the “producing code” and the “consuming code” together. In terms of our analogy: this is the “subscription list”. The “producing code” takes whatever time it needs to produce the promised result, and the “promise” makes that result available to all of the subscribed code when it’s ready.

6. developer.mozilla.org › en-US › docsHow to use promises - Learn web development | MDN

   developer.mozilla.org › en-US › docs

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   May 31, 2024 · Promises are the foundation of asynchronous programming in modern JavaScript. They make it easier to express and reason about sequences of asynchronous operations without deeply nested callbacks, and they support a style of error handling that is similar to the synchronous try...catch statement.

7. www.freecodecamp.org › news › guide-to-javascript-promisesHow Promises Work in JavaScript – A Comprehensive Beginner's...

   www.freecodecamp.org › news › guide-to-javascript-promises

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   Jun 13, 2023 · This article is an in-depth guide to promises in JavaScript. You are going to learn why JavaScript has promises, what a promise is, and how to work with it. You are also going to learn how to use async/await—a feature derived from promises—and what a job queue is. Here are the topics we will cover: Why should you care about promises?

8. www.javascripttutorial.net › es6 › javascript-promisesJavaScript Promises - JavaScript Tutorial

   www.javascripttutorial.net › es6 › javascript-promises

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   In this tutorial, you will learn about JavaScript promises and how to use them effectively in asynchronous programming.

9. javascript.info › promise-apiPromise API - The Modern JavaScript Tutorial

   javascript.info › promise-api

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   Feb 20, 2022 · Promise API. The JavaScript language. Promises, async/await. February 20, 2022. Promise API. There are 6 static methods in the Promise class. We’ll quickly cover their use cases here. Promise.all. Let’s say we want many promises to execute in parallel and wait until all of them are ready.

10. www.freecodecamp.org › news › javascript-promises-async-await-and-promise-methodsHow to Use JavaScript Promises – Callbacks, Async/Await, and ...

    www.freecodecamp.org › news › javascript-promises-async-await-and-promise-methods

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    Aug 15, 2023 · Promises are one of the most important parts of JavaScript – but they can be confusing and difficult to understand. Many new devs, as well as experienced ones, struggle to fully grasp them. So what is a promise? A promise represents an asynchronous operation whose result will come in the future.

11. www.freecodecamp.org › news › javascript-promises-explainedJavaScript Promises Explained - freeCodeCamp.org

    www.freecodecamp.org › news › javascript-promises-explained

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    Jan 15, 2020 · What is a promise in JavaScript? JavaScript is single threaded, meaning that two bits of script cannot run at the same time; they have to run one after another. A Promise is an object that represents the eventual completion (or failure) of an asynchronous operation, and its resulting value.