var promise = new Promise(function(resolve, reject) {
// do some long running async thing…
if (/* everything turned out fine */) {
resolve("Stuff worked!");
}
else {
reject(Error("It broke"));
}
});
//usage
promise.then(
function(result) { /* handle a successful result */ },
function(error) { /* handle an error */ }
);Promises make async javascript easier as they are easy to use and write than callbacks. Basically , promise is just an object , that gives us either success of async opertion or failue of async operationsA promise is an object that may produce a single value sometime in the future: either a resolved value, or a reason that it's not resolved (e.g., a network error occurred)myPromise
.then(handleResolvedA)
.then(handleResolvedB)
.then(handleResolvedC)
.catch(handleRejectedAny)
.finally(handleComplition)
Method Description
all(iterable) Waits for all promises to be resolved or any one to be rejected
allSettled(iterable) Waits until all promises are either resolved or rejected
any(iterable) Returns the promise value as soon as any one of the promises is fulfilled
race(iterable) Wait until any of the promises is resolved or rejected
reject(reason) Returns a new Promise object that is rejected for the given reason
resolve(value) Returns a new Promise object that is resolved with the given value
catch() Appends the rejection handler callback
then() Appends the resolved handler callback
finally() Appends a handler to the promise