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
new Promise( (res, rej) => { setTimeout(() => res(1), 1000); }).then( (res) => { console.log(res); // 1 return res*2 }).then( (res) => { console.log(res); // 2 });
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 */ } );
promise javascript
let promise = new Promise(function(resolve, reject){ try{ resolve("works"); //if works } catch(err){ reject(err); //doesn't work } }).then(alert, console.log); // if doesn't work, then console.log it, if it does, then alert "works"
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) => { });
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
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