program2.js

//you can run this program by using the command =>   node program2.js

// keywords -> reserved words for specific reasons. example -> for,while, do while, if, else, else if, break, try,catch, function, var, const, let etc.

// data type
// primitive data type - String, Number (int,float,double), Boolean, Undefined, Null
// Reference data type - Array, Object.
// use typeof() to check the data type
// comment -> single line comment, double line comment

//This is a single line comment

/*
This is 
multiple line
comment
*/

console.log(typeof 123);
console.log(typeof 123.5);
console.log(typeof "123");
console.log(typeof true);
console.log(typeof false);

//collected from w3school's website
var car; // Value is undefined, type is undefined
var car = ""; // The value is "", the typeof is "string"

var person = { firstName: "John", lastName: "Doe", age: 50, eyeColor: "blue" };
person = null; // Now value is null, but type is still an object

var person = { firstName: "John", lastName: "Doe", age: 50, eyeColor: "blue" };
person = undefined; // Now both value and type is undefined

typeof "John"; // Returns "string"
typeof 3.14; // Returns "number"
typeof true; // Returns "boolean"
typeof false; // Returns "boolean"
typeof x; // Returns "undefined" (if x has no value)