This keyword

The this keyword returns the value of the context where it's called, in a regular function the this keyword points at the global object, (the window object in the browser). in a method (function in object) this points to the object that it's calling.

This in a regular function

function calculateAge(year) {
    console.log( 2018 - year );
    console.log(this);
}

In this example we use this in a regular function so the value of this will be the window object because we call this in a regular function.

Note: - With ES6 and arrow functions the this keyword will point to the actual function.

This in an object

let perso = {
    name: John,
    yearOfBirth: 1995,
    calculateAge: function () {
        console.log(this);
    }
}

In this example we use the this keyword in an method so it will returns the perso object.

Function in a method

let perso = {
    name: John,
    yearOfBirth: 1995,
    calculateAge: function () {
        console.log(this);

        function innerFunction () {
            console.log(this);
        }
        innerFunction();
    }
}

This time we call a regular function inside a method so the this keyword will return the window object because it's still a regular function.

Current errors

This is a list of the main errors that you can meet when you use this keyword:

Note: I'm not a wizard there is maybe some issue that you notice above so fell free to open an issue in the github repo if you find a new error not mentioned above.