ES6 Arrow function is changing the scope of this in Meteor.publish [duplicate]

This question already has an answer here:

What does “this” refer to in arrow functions in ES6? 7 answers

So I been started using ES6 in Meteor, but apparently if you try to use Meteor.publish syntax with an arrow function, this.userId is undefined, while if you use it with a regular function(){} this.userId works perfectly, Im assuming is a kind of transpiler process that assign a different this, to userId but is just a guess, does anyone knows what really is happening?

Meteor.startup(function() {
    Meteor.publish("Activities", function() { //with function
        console.log(this.userId); //TS8vTE3z56LLcaCb5
    });
});

Meteor.startup(function() {
    Meteor.publish("Activities", ()=> { //with arrow function
        console.log(this.userId); //undefined
    });
});

This isn't a transpilation error, it's a feature of arrow functions. The arrow function automatically sets the context of the function body to the contexts here it was created, in this case the callback to Meteor.publish. This prevents Meteor from rebinding the context of your listener function.

From the Meteor publish docs: