use a promise in javascript code example

Example 1: 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 2: js return a promise

function myAsyncFunction(url) {
  return new Promise((resolve, reject) => {
    const xhr = new XMLHttpRequest();
    xhr.open("GET", url);
    xhr.onload = () => resolve(xhr.responseText);
    xhr.onerror = () => reject(xhr.statusText);
    xhr.send();
  });
}

Example 3: making promises in js

getData()
    .then(data => console.log(data))
    .catch(error => console.log(error));