Basic JS concepts: https://wesbos.com/courses/
V8 = JS engine for Chrome
SpiderMonkey = JS engine for Mozilla
Node.js = run-time environment written in C++
document.querySelector(#id .class)
Falsy values : undefined, null '', false, 0, NaN
Truthy: 1, 'some_string'
Strict Eq "===" have the same value and type
Loose Eq "==" have same value but can be different type '1' == 1