some issues with Promise

[mattdesl]

I think promise is a pretty big section that should probably be split into its own lesson

Some issues I'm seeing:

• we should encourage reject(new Error('str')) rather than rejecting with strings
• we should encourage capitalizing Promise constructor
• Promise.reduce() and catching SyntaxError is not part of the Promise spec; I guess we should decide whether the lesson uses simple ES6 promises, or Bluebird, or a bit of both
• .then(onResolve, onReject) should be described a bit
• memoization seems like a bit of an advanced pattern, I think it's generally not needed and might just confuse students as they are trying to learn the basics
• Promise.resolve, Promise.reject and Promise.all should be described somewhere
• instead of using reduce the last examples should be using map (reduce is used when you want to resolve to a single value, e.g. getting the max width of all loaded images)

for e.g.

var images = Promise.map(imageArray, loadImage);
images.then(renderImages);

Or with ES6:

var images = Promise.all(imageArray.map(loadImage));

Or with error handling:

var notFoundImage = loadImage('notfound.png')

var images = Promise.map(imageArray, function(file) {
  return loadImage(file)
    .then(null, function(err) {
      return notFoundImage
    })
})

[mattdesl]

Not sure if these and the other PRs flew under the radar. Should I merge?

[mikkoh]

Yeah for some reason I hadn't even seen em. I merged.