how to use promises in javascript code example
Example 1: 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);
});
});
Example 2: javascript promise
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 */ }
);
Example 3: promise javascript
const promiseA = new Promise( (resolutionFunc,rejectionFunc) => {
resolutionFunc(777);
});
// At this point, "promiseA" is already settled.
promiseA.then( (val) => console.log("asynchronous logging has val:",val) );
console.log("immediate logging");
// produces output in this order:
// immediate logging
// asynchronous logging has val: 777
Example 4: making promises in js
getData()
.then(data => console.log(data))
.catch(error => console.log(error));
Example 5: 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) => {
});