Javascript promise

promise_demo_1.js

// http://jsfiddle.net/mkjh2ev5/1245/

let cleanRoom = function() {
  return new Promise(function(resolve, reject) {
    resolve('Cleaned The Room');
  });
};

let removeGarbage = function(message) {
  return new Promise(function(resolve, reject) {
    reject(message + ' remove Garbage');
  });
};

let winIcecream = function(message) {
  return new Promise(function(resolve, reject) {
    resolve( message + ' won Icecream');
  });
};

Promise.all(
 [cleanRoom(), 
  removeGarbage(),
  winIcecream()]
).then(function (arr) {
	console.log(arr)
}).catch(function (err) {
	console.log(`Error: ${err}`);
})

cleanRoom().then(function(result){
  console.log("Success")
	return removeGarbage(result);
}).then(function(result){
	return winIcecream(result);
}).then(function(result){
	console.log('finished ' + result);
}).catch(function(error){
	console.log(`Error: ${error}`);
})

promise_vs_callback.js

// https://www.youtube.com/watch?v=2d7s3spWAzo&list=PL0zVEGEvSaeEd9hlmCXrk5yUyqUag-n84
let addImg = (src) => {
  let imgElement =
    document.createElement("img")
  imgElement.src = src
  document.body.appendChild(imgElement)
}

// promise implementation
function loadImage(url) {
  return new Promise((resolve, reject) => {
    let image = new Image()

    image.onload = function() {
      resolve(image)
    }

    image.onerror = function() {
      let message =
        'Could not load image at ' + url
      reject(new Error(message))
    }

    image.src = url

  })
}

Promise.all([
  loadImage('images/cat1.jpg'),
  loadImage('images/cat.jpg'),
  loadImage('images/cat3.jpg'),
  loadImage('images/cat4.jpg')
]).then((images) => {
  console.log(images)
  images.forEach(img => addImg(img.src))
}).catch((error) => {
  // handle error later
  console.log(error)
})

// callback implementation
function loadImageWithCallback(url, callback) {
  let image = new Image()

  image.onload = function () {
    callback(null, image)
  }

  image.onerror = function () {
    let message = 
      'Could not load image at: ' + url
    callback(new Error(message))
  }

  image.src = url
}

loadImageWithCallback('images/cat1.jpg', (error, img1) => {
  if(error) throw error;
  addImg(img1.src)
  loadImageWithCallback('images/cat2.jpg', (error, img2) => {
    if(error) throw error;
    addImg(img2.src)
    loadImageWithCallback('images/cat3.jpg', (error, img3) => {
      if(error) throw error;
      addImg(img3.src)
    })
  })
})