"You don't know JS" series dedicated the whole book to "this" mystery : https://github.com/getify/You-Dont-Know-JS/blob/master/this%20&%20object%20prototypes/RE

"You don't know JS" series dedicated the whole book to "this" mystery : https://github.com/getify/You-Dont-Know-JS/blob/master/this%20&%20object%20prototypes/README.md#you-dont-know-js-this--object-prototypes https://github.com/getify/You-Dont-Know-JS/blob/master/this%... Read this, 3 times maybe, and you will become the master of this.