var, let, and const are use to declare variables.
var can be re-declaration and updates within the same scope.
let allowing updates but not re-declaration within the same block.
const cannot be reassigned.

In JS map(), forEach(), and filter() are array methods.

forEach() do not return anything thats why we do not need to declare any variable and it will not change the original array
and returns undefined.
map() executes the same code on every element in an array and returns a new array with the transformed values,
It will not change the original array.
filter() method receives function as a parameter. filter()method will return an array of matching elements
else will return an empty array if no matching happens. It will not change the original array.

Arrow function is shorter compare with regular function and it cannot be accessed before initialization.
Regular functions have access to the arguments object. Arrow functions do not have access to the arguments object.
Regular functions have their own this binding. Arrow functions don't have their own this binding, arguments object, or prototype.

A Promise is a JavaScript object that will produce a single value at some point in the future.
If the promise is fulfilled, it will provide a resolved value; if not, it will return a cause for the failure.
It is used for handling asynchronous operations, such as making API calls or reading files, in a more organized and readable way.
Promises have three states: Pending, Fulfilled and Rejected.
Promises have two main methods: then(), catch().

A closure is the combination of a function bundled together with references to its surrounding state.
In other words, a closure gives a function access to its outer scope. Closures are created every time a function is created,
at run time. Closure is just a fancy name for a function that remembers the external things used inside it.