1// `let` vs `var` vs `const` in 'javascript'
2
3"let" allows you to declare local variable whose scope 
4      is limited to the block statement.
5
6"var" allows you to declare a variable globally or locally 
7      to an entire function.
8
9"Const" just like let, are block-scoped.
10        It's value can't be reassigned and it can't be redeclared.
11

1//Making variables with let:
2let numberOfFriends = 1;
3
4//Incrementing:
5numberOfFriends += 3; //numberOfFriends is now 4
6
7// Variables with const
8const minimumAge = 21; //CANNOT REASSIGN!
9
10//Booleans - true or false values
11true;
12false;
13let isHappy = true;
14
15//Naming Conventions
16// Use upper camel-cased names:
17let numberOfChickens = 6; //GOOD
18// NOT THE JS WAY:
19// let number_of_chickens = 6;

1var Hello = "World";
2let bool = false;
3const int = 8788;

1var a;
2console.log(a);                // scrive in console "undefined" o "" a seconda del browser usato.
3console.log('still going...'); // scrive in console "still going...".

1var is a keyword to define the varible in js but as of es-6 we, use let and const keywords for the same

1var example = "hello";
2document.write(example);// it will say hello when it runs