JavaScript-Blog 2

We will learn about

• Display Output
• Data Types
• Comments
• Variables
• Operators and its types

First JS program

“console.log” is used to log (print) something on the console(screen).

console.log("Hello World!");

Output:

Hello World!

Any thing written inside the Quotation Mark (“”) will be displayed on screen.

Data Types in JS

We store different types of data.

• Numbers, e.g. 123, 120.50 etc.
• Strings of text e.g. “This text string”, name etc.
• Boolean e.g. true or false.
• There are other data types which we will discuss later like null, undefined, symbol etc

Comments

Single Line Comments

Single line comments start with //.

Any text between // and the end of the line will be ignored by JavaScript (will not be executed).

Multi-line Comments

Multi-line comments start with /* and end with */.

Any text between /* and */ will be ignored by JavaScript.

Variables

Variables are containers that store data. Variables are used to store information to be referenced and manipulated in a computer program. They also provide a way of labeling data with a descriptive name, so our programs can be understood more clearly by the reader and ourselves.

JavaScript Variables can be declared in 4 ways:

• Automatically
• var: Variables can be redeclared and updated. A global scope variable.
• let: Variables can not be redeclared but can be updated. A block scope variable.
• const: Variables can not be redeclared and updated. A block scope variable.

var is used rarely. We use let and const to declare variables.

Variable Rules:

• Variable names are case sensitive. “a” and “A” is different.
• Variable names must start with a letter, an underscore (_) or a dollar sign ($).
• Variable names cannot contain spaces.
• Variables cannot be the same as reserved keywords such as if or const.
• Variables should be given descriptive names that indicate their content and usage (e.g. sellingPrice and costPrice rather than x and y).
• By convention, JavaScript variable names are written in camelCase.

Code:

let age = 24;                           // number
console.log(age);

let name = "tony stark";                // string
console.log(name);

let isEmpty = true;                     // boolean 
console.log(isEmpty);

const PI = 3.14;
console.log(PI);

Output:

24
tony stark
true
3.14

Operators

Operators are used to perform operations on data stored in variables.

JavaScript supports the following types of operators.

• Arithmetic Operators
• Comparison Operators
• Logical (or Relational) Operators
• Assignment Operators
• Conditional (or ternary) Operators

Arithmetic Operators

Common mathematical operations

Operator	Description
+	Addition
–	Subtraction
*	Multiplication
**	Exponentiation (ES2016)
/	Division
%	Modulus (Division Remainder)

Code:

let a = 5;
let b = 3;
let c = a + b;
let d = a - b;

console.log("a + b = ", c);
console.log("a - b = ", d);
console.log("a * b = ", a*b);
console.log("a / b = ", a/b);
console.log("a % b = ", a%b);       // gives reminder
console.log("a ** b = ", a**b);     // 5^2

Output:

a + b =  8
a - b =  2
a * b =  15
a / b =  1.6666666666666667
a % b =  2
a ** b =  125

Unary Operators

Unary operator requires only one operand to work.

Operator	Description
++	increment (value is incremented by 1)
—	decrement (value is decremented by 1)

Code:

let x = 5 , y = 5;
x = x + 1;      
console.log("x = ", x); 

y++;                     // post increment: same as y = y + 1
console.log("y = ", y); 
--y;                     // pre increment: same as y--
console.log( "y = " , y); 

Output:

x =  6
y =  6
y =  5

Assignment Operators

Assignment operators assign values to JavaScript variables.

Operator	Example	Same As
=	x = y	x = y
+=	x += y	x = x + y
-=	x -= y	x = x – y
*=	x *= y	x = x * y
/=	x /= y	x = x / y
%=	x %= y	x = x % y
**=	x **= y	x = x ** y

Code:

let a = 5, b = 2;

a += b;
console.log("a = ", a); 

b **= b;                //2^2
console.log("b = ", b);

Output:

a =  7
b =  4

Comparison Operators

Compare values and return true or false

Operator	Description
==	equal to
===	equal value and equal type
!=	not equal
!==	not equal value or not equal type
>	greater than
<	less than
>=	greater than or equal to
<=	less than or equal to

Code:

let a = 5, b = 2;       //numbers
let c = "5";            //string
console.log("a == b ", a==b);
console.log("a == c ", a==c);
console.log("a === c ", a===c);

Output:

a == b  false
a == c  true
a === c  false

Logical Operators

&&                  LOGICAL AND returns true if both statements are true        

||                   LOGICAL OR returns true if one of the statements is true      

!                    LOGICAL NOT reverse the result, returns false if the result is true

Code:

let x = 6;
let cond1 = x > 5;      //true
let cond2 = x === 6;    //true
console.log("cond1 && cond2", cond1 && cond2);

console.log((x < 5 &&  x < 10));
console.log((x < 4 || x < 10) );
console.log(!(x < 5 && x < 10));

Output:

cond1 && cond2 true
false
true
true