Still need to learn TypeScript later.

Basic

JS does automatic type coercion, so 3/4=0.75

== performs type conversion during comparison. === (strict equal) does not perform type conversion.

var is function/global scoped, let and const are block scoped.

Array Methods

map() creates a new array with results of calling a function on every element.

reduce() executes a reducer function on each element, accumulating to a single value.

About this

this is dynamically bound to the parent context. If extracted from an object, it becomes undefined.