Methods in Es6 Objects: Using Arrow Functions

Methods in ES6 objects: using arrow functions

Arrow functions are not designed to be used in every situation merely as a shorter version of old-fashioned functions. They are not intended to replace function syntax using the function keyword. The most common use case for arrow functions is as short "lambdas" which do not redefine this, often used when passing a function as a callback to some function.

Arrow functions cannot be used to write object methods because, as you have found, since arrow functions close over the this of the lexically enclosing context, the this within the arrow is the one that was current where you defined the object. Which is to say:

// Whatever `this` is here...
var chopper = {
    owner: 'Zed',
    getOwner: () => {
        return this.owner;    // ...is what `this` is here.
    }
};

In your case, wanting to write a method on an object, you should simply use traditional function syntax, or the method syntax introduced in ES6:

var chopper = {
    owner: 'Zed',
    getOwner: function() {
        return this.owner;
    }
};

// or

var chopper = {
    owner: 'Zed',
    getOwner() {
        return this.owner;
    }
};

(There are small differences between them, but they're only important if you use super in getOwner, which you aren't, or if you copy getOwner to another object.)

There was some debate on the es6 mailing list about a twist on arrow functions which have similar syntax but with their own this. However, this proposal was poorly received because that is mere syntax sugar, allowing people to save typing a few characters, and provides no new functionality over existing function syntax. See the topic unbound arrow functions.

Arrow Function Created In An Object Returns undefined When Called Using .call() Method

Arrow functions don't bind to this as function do. That's one of the main reason they were introduced (probably the most important one).

You cannot even bind them.

ES6 Arrow function: why this points differently when used in constructor and object literal?

function Obj() {
  this.show = () => {
    console.log(this);
  };
}
const o = new Obj();
o.show(); 

Here "this" works based on the rules of the "new" keyword, pointing to a new object with the structure defined inside Obj() (the new object is the context).
More info at : https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/new

const o2 = {
  show: () => {
    console.log(this);
  }
}
o2.show() // window || undefinded

Here "this" gets its value at runtime and because neither lambda functions nor object literals define a context, the context remaining is the global one and that is why you get that value.

this keyword in arrow function

Arrow functions have a lexical this which means that the value of this inside the function is the same as the value of this outside the function.

It does not mean that this points to an object containing all the variables from outside the function.

const anObject = {
  aValue: "example value",
  aMethod: function() {
    console.log("aMethod", this.aValue);

    const arrow = () => {
      console.log("arrow", this.aValue);
    }
    
    arrow();
  }
}

anObject.aMethod();

const copyOfAMethod = anObject.aMethod;
copyOfAMethod();

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