How to use promises - Learn web development | MDN

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• ation. At the time the promise is returned to the caller, the operation often isn't finished, but the promise object provides methods to handle the eventual success or failure of the operation.

• A promise is an object returned by an asynchronous function, which represents the current state of the operation

• then() itself returns a promise

• Inside an async function, you can use the await keyword before a call to a function that returns a promise. This makes the code wait at that point until the promise is settled, at which point the fulfilled value of the promise is treated as a return value, or the rejected value is thrown

• all

• If you add catch() to the end of a promise chain, then it will be called when any of the asynchronous function calls fails.

• First, a promise can be in one of three states:

• pending

• fulfilled

• rejected

• async and await

• Adding async at the start of a function makes it an async function

• Inside an async function, you can use the await keyword before a call to a function that returns a promise.

• completed with the result of the function passed to it

• what "succeeded" or "failed" means here is up to the API

• pending: the promise has been created, and the asynchronous function it's associated with has not succeeded or failed yet

• then() handler

• fetch() API

• 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