I have an easy way of declaring constants and variables (integer, string, arrays etc). Why? 

• I am dynamically typed language (means you don't have to worry about the type of variable like integer, string etc. I will do it for you at runtime).
• I provide 3 keywords const, var, let  to declare variables. 

1- var (MDN)

//This is how you can write a comment

var myNameInString = "JavaScript";    //this is string
var myNameInArray = ['J','a','v','a','S','c','r','i','p','t'];     //this is array
var myBirthdayYear = 1995;      // this is number

// below is an object
var myDetails = {     
     name: "JavaScript",
     creator: "Brendan Eich"
}    

console.log(myNameInString);           //JavaScript


//console.log() is use to print the result of an expression

myNameInString = "My name is Javascript";

console.log(myName);          //My name is Javascript

As I previously mentioned that I am dynamically typed so you can use only var to declare all type of variables.  Try it on JSBin

2- const (MDN)

const myName = "JavaScript"

console.log(myName);        //JavaScript

myName = "My Name is JavaScript";       // this will throw error

const is like constant. Once you declare and define, then you can't change the value of that constant (myName in our case) thereafter. 

3- let (MDN)

let myName = "JavaScript"

console.log(myName);        //JavaScript

myName = "My Name is JavaScript";       // My Name is JavaScript

let works similar to var but let is block scoped. (block-scoped is an advanced feature and you can read on MDN).

Note: Just use const for constants and let for variables instead of var.