https://toddmotto.com/everything-you-wanted-to-know-about-javascript-scope/
https://www.sitepoint.com/demystifying-javascript-variable-scope-hoisting/
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference