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Promises are used in JavaScript to handle the state of a Promise. They are special objects that link the actual output and the reason due to which we may not get the output. Promises can be a bit of hectic stuff if you don't have experience with callbacks and callback hells. Once you grasp this concept, there is no going back! The then and catch clauses can be used to create a promise. The promise constructor is a callback of the promise constructor. It takes two callbacks: resolve and reject callbacks. It sends the value sent through method as an argument.