promise test

promise.js

const log = (text) => {
  if (text instanceof Error) {
    text = "ERROR: " + text.message;
  }
  document.querySelector("#log").textContent += "\n" + JSON.stringify(text, null, 4);
}

const randomTime = () => Math.round(Math.random() * 1000);

const notNull = item => item !== null;

const getThumb = function(id) {
  if (id === 3) {
    return null;
  }
  return "http://some.link/image-" + id + ".jpg";
}

const getThumbAsync = function(id) {
  return new Promise((resolve, reject) => {
    if (id === 3) {
      reject(new Error("cant get thumb"));
      return;
    }
    if (id === 4) {
      resolve("http://async-" + id + ".jpg");
      return;
    }
    setTimeout(() => resolve("http://async-" + id + ".jpg"), randomTime());
  });
}

const ids = [1, 2, 3, 4];

const getThumbs = (items) => {
  return items.map(getThumb).filter(notNull);
}