Promises Terms in JavaScript

  •  Promise Chaining
    • Instead of calling the second .then() inside the handler for the first .then(), we can return the promise returned by json(), and call the second .then() on that return value.

  • Catching errors in Promise:
    • To support error handling, Promise objects provides a .catch()method.
    • It is very simple to remember: when asynchronous operation succeeds, .then() is called whereas when it fails, the handler is passed to .catch().
    • If we add .catch()to the end of a promise chain, then it will be called when any one of the .then() method fails in the chain.


  • States of promise:
    • pending: the promise has been created and the function has neither succeeded nor failed.
    • fulfilled: the asynchronous function has succeeded. When a promise is fulfilled, its .then() handler is called.
    • rejected: the asynchronous function has failed. When a promise is rejected, its .catch() handler is called.
    • settled: to cover both fulfilled and rejected states.
    • resolved: if its settled







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