7 DataTypes.js

//JavaScript Data Types

let length = 16;                               // Number
let lastName = "Johnson";                      // String
let x = {firstName:"John", lastName:"Doe"};    // Object 

/*
***********JavaScript Types are Dynamic*************

JavaScript has dynamic types. This means that the same variable can be used to hold different data types:
*/
{
let x;           // Now x is undefined
x = 5;           // Now x is a Number
x = "John";      // Now x is a String 
}
/*
*************JavaScript Strings************

A string (or a text string) is a series of characters like "John Doe".

Strings are written with quotes. You can use single or double quotes:


*/
let carName1 = "Volvo XC60";   // Using double quotes
let carName2 = 'Volvo XC60';   // Using single quotes 

let answer1 = "It's alright";             // Single quote inside double quotes
let answer2 = "He is called 'Johnny'";    // Single quotes inside double quotes
let answer3 = 'He is called "Johnny"';    // Double quotes inside single quotes 

/*
*********JavaScript Numbers***********

JavaScript has only one type of numbers.

Numbers can be written with, or without decimals:
*/
let x1 = 34.00;     // Written with decimals
let x2 = 34;        // Written without decimals 

/*
Extra large or extra small numbers can be written with scientific (exponential) notation:
*/
let y = 123e5;      // 12300000
let z = 123e-5;     // 0.00123 

/*
*********JavaScript Booleans************

Booleans can only have two values: true or false.
*/
{
    let x = 5;
    let y = 5;
    let z = 6;
    //(x == y)       // Returns true
   // (x == z)       // Returns false 

}
/*
**********JavaScript Arrays*************

JavaScript arrays are written with square brackets.

Array items are separated by commas.

The following code declares (creates) an array called cars, containing three items (car names):
*/
const cars = ["Saab", "Volvo", "BMW"];

//Array indexes are zero-based, which means the first item is [0], second is [1], and so on.

/*
***************JavaScript Objects*************

JavaScript objects are written with curly braces {}.

Object properties are written as name:value pairs, separated by commas.

*/
const person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};
//The object (person) in the example above has 4 properties: firstName, lastName, age, and eyeColor.

/*
***************The typeof Operator*************

You can use the JavaScript typeof operator to find the type of a JavaScript variable.

The typeof operator returns the type of a variable or an expression:
*/

typeof ""             // Returns "string"
typeof "John"         // Returns "string"
typeof "John Doe"     // Returns "string" 
typeof 0              // Returns "number"
typeof 314            // Returns "number"
typeof 3.14           // Returns "number"
typeof (3)            // Returns "number"
typeof (3 + 4)        // Returns "number" 

/*
***********Undefined***************

In JavaScript, a variable without a value, has the value undefined. The type is also undefined.
*/
let car;    // Value is undefined, type is undefined

//Any variable can be emptied, by setting the value to undefined. The type will also be undefined

car = undefined;    // Value is undefined, type is undefined 

/*
Empty Values

An empty value has nothing to do with undefined.

An empty string has both a legal value and a type.
*/
{
let car = "";    // The value is "", the typeof is "string" 
}