javascript promises
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 */ }
);new promise function
const myPromise = new Promise((resolve, reject) => {
setTimeout(() => {
resolve('foo');
}, 300);
});
myPromise
.then(handleResolvedA, handleRejectedA)
.then(handleResolvedB, handleRejectedB)
.then(handleResolvedC, handleRejectedC);twhat is a js promise
const promise1 = new Promise((resolve, reject) => {
setTimeout(() => {
resolve('foo');
}, 300);
});
promise1.then((value) => {
console.log(value);
// expected output: "foo"
});
console.log(promise1);
// expected output: [object Promise]what is promise in javascript
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 operationspromise definition in javascript
A 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)promise javascript
/*
Promise is a constructor function, so you need to use the new keyword to
create one. It takes a function, as its argument, with two parameters -
resolve and reject. These are methods used to determine the outcome of the
promise.
The syntax looks like this:
*/
const myPromise = new Promise((resolve, reject) => {
});Copyright © 2021 Codeinu
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