js create a promise
/*
A Promise is a proxy for a value not necessarily known when the promise is created.
It allows you to associate handlers with an asynchronous action's eventual success
value or failure reason.
*/
let promise = new Promise((resolve , reject) => {
fetch("https://myAPI")
.then((res) => {
// successfully got data
resolve(res);
})
.catch((err) => {
// an error occured
reject(err);
});
});promise catch
//create a Promise
var p1 = new Promise(function(resolve, reject) {
resolve("Success");
});
//Execute the body of the promise which call resolve
//So it execute then, inside then there's a throw
//that get capture by catch
p1.then(function(value) {
console.log(value); // "Success!"
throw "oh, no!";
}).catch(function(e) {
console.log(e); // "oh, no!"
});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 */ }
);javascript create promise
// base case
const promise = new Promise(executor);
// more complex example
const coinflip = (bet) => new Promise((resolve, reject) => {
const hasWon = Math.random() > 0.5 ? true : false;
if (hasWon) {
setTimeout(() => {
resolve(bet * 2);
}, 2000);
} else {
reject(new Error("You lost...")); // same as -> throw new Error ("You lost ...");
}
});new promise function
const myPromise = new Promise((resolve, reject) => {
setTimeout(() => {
resolve('foo');
}, 300);
});
myPromise
.then(handleResolvedA, handleRejectedA)
.then(handleResolvedB, handleRejectedB)
.then(handleResolvedC, handleRejectedC);promises in javascript
myPromise.then(
function(value) { /* code if successful */ },
function(error) { /* code if some error */ }
);Copyright © 2021 Codeinu
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