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The readme should also link to http://knpuniversity.com/screencast/javascript-es6

I'm talking about this chapter: knpuniversity.com/screencast/javascript-es6/set-object

currently, the description looks like this:

The Map object is perfect for maps, or associative arrays as we call them in the PHP biz. ES2015 gives us another object called Set. This new fancy object replaces using true, indexed arrays.
// ...
ep - the Set object is just like an array, but with some helper methods! Back up in loadRepLogs, after the for loop, let's see how this looks: console.log(this.repLogs). Oh, and let's also use one of its helper methods: this.repLogs.has(data.items[0]). Obviously, this item should have been added to the Set!

This description is wrong. Set and Array are totally different data structures:

• Array is the ES representation of a sequence (and btw, it is an object with helper methods. you might like Array.prototype.includes in ES2016 for the example used in your current description)
• Set is the ES representation of ... a set, i.e. a data structure ensuring uniqueness of values in it.

The case of repLogs is a use case for Array, not for Set.

When you need both keys and values during the iteration over a Map, there is an easy way to do it with for of:

for (let [key, value] of myMap.entries()) {
// do something
}

This is much better than using for in, which is looping over iterable properties of the Map object (which won't do what you expect here).

Btw, Array has this method too in ES2015, in case you need to access both the value and the integer index (requires a polyfill for IE, of course).

Array, Map and Set are big friends in ES2015.

On production enviroment i get this:

Oops! An Error Occurred
The server returned a "500 Internal Server Error".
Something is broken. Please let us know what you were doing when this error occurred. We will fix it as soon as possible. Sorry for any inconvenience caused.

On development enviroment i get this:

Class "fos_user.model.user.class" not found. Is the "data_class" form option set correctly?
500 Internal Server Error - InvalidArgumentException

Any comments ?