Variables, Datatypes and Operators, Conditional Statement, and Loops in JavaScript.

Identifiers:

Identifiers are those names that help in naming the elements in JavaScript.

Set of rules, you should follow to write an Identifiers:

1. The first character of an identifier should be letters of the alphabet or an underscore (_) or dollar sign ($).
2. You can use letters of alphabets or digits or underscores (_) or a dollar sign ($) to an Identifiers.
3. Identifiers are case-sensitive. so, name and Name are not the same.

Note: You can’t use Reserved keywords as Identifiers.

Types of Identifiers (based on scope of the identifier and the data which an identifier will hold):

Data Types:

• JavaScript language is a loosely typed or dynamically typed language.
• The data is said to be primitive if it contains an individual value.

Number:

• In JavaScript, any other value that does not belong to the above-mentioned types is not considered as a legal number. Such values are represented as NaN (Not-a-Number).

String:

• String values are written in quotes, either single or double (like python).

• To access any character within the string, it is important to be aware of its position in the string.
• The first character exists at index 0, next at index 1, and so on.

Literals:

• Literals can span multiple lines and interpolate expressions to include their results.

Boolean:

• Boolean is a data type which represents only two values: true and false.
• Example: 100, -5, “Cat”, 10<20, 1, 10*20+30, etc. evaluates to true whereas, 0, “”, NaN, undefined, null, etc. evaluates to false.

Undefined:

• When the variable is used to store “no value”, primitive data type undefined is used.

null:

• The null value represents “no object”.
• Null data type is required as JavaScript variable intended to be assigned with the object at a later point in the program can be assigned null during the declaration.

Bigint:

• BigInt is a special numeric type that provides support for integers of random length.
• A BigInt is generated by appending n to the end of an integer literal or by calling the function BigInt that generates BigInt from strings, numbers, etc.

Symbol:

• A “symbol” represents a unique identifier. You can make use of Symbol() to generate a value of this type.

Example:

• Even if various symbols are created with the same description, they are different values. Thus, symbols ensures uniqueness. So the description provided can be considered as just a label.
• Strings and symbols are basically different and should not accidentally get converted to the other one.
• So far you know that symbols remain unique even if they have the same name. But at times, there may be a situation where you may want the symbols with same name to be same entities.

Then use global Symbols.

Non-Primitive Datatypes:

• The data type is said to be non-primitive if it is a collection of multiple values.
• JavaScript gives non-primitive data types named Object and Array, to implement this.

Objects:

Objects in JavaScript are a collection of properties and are represented in the form of [key-value pairs].

• The ‘key’ of a property is a string or a symbol and should be a legal identifier.
• The ‘value’ of a property can be any JavaScript value like Number, String, Boolean, or another object.

Syntax:

Example:

Array:

The Array is a special data structure that is used to store an ordered collection, which cannot be achieved using the objects.

• How to declare an Array in JavaScript:

• A single array can hold multiple values of different data types.

Operators:

• Operators are categorized into unary, binary, and ternary based on the number of operands on which they operate in an expression.

typeOf :

• “typeOf” is an operator in javaScript.

Example of typeOf:

👉 Statements:

⇨ Statements are instructions in JavaScript that have to be executed by a web browser.

⇨ JavaScript code is made up of a sequence of statements and is executed in the same order as they are written.

⇨ A Variable declaration is the simplest example of a JavaScript statement.

⇨ Other types of JavaScript statements include conditions/decision making, loops, etc.

⇨ White (blank) spaces in statements are ignored.

• Non-Conditional statements are those statements that do not need any condition to control the program execution flow.

In JavaScript, it can be broadly classified into three categories as follows:

Comments:

// Single line Comment

/*
* Multi-Line 
      Comment
*/

Conditional Statements:

In JavaScript, there are three forms of the if...else statement.

1. if statement
2. if…else statement
3. if…else if…else statement

if statement:

Syntax:

if (condition) {  // if condition is True then Body of If will run
    // the body of if
}

Example:

let num = 5;
if(num > 3){
    console.log("number is greater than 3");
}
console.log("Number is lesser than 3");

If…else statement:

Syntax:

if (condition) {
    // the body of if
} else {
    // body of else 
}

Working of if…else statement:

Example:

let num = 2;
if(num % 2 == 0){
  console.log( num," is Even Number" );
} else {
  console.log(num," is Odd Number" );
}

Similarly, if….else…if will work.

Ternary operator:

• It is also using as conditional statement.
• ternary operator is the only conditional operator that takes three operands.

Example:

let num = 5;
(num % 2 == 0) ? console.log("Number is Even.") : console.log("Number is Odd.");

Switch-Case:

• You can use a switch-case statement in place of if…else…if statement.
• Switch-case does so more efficiently than repeated if…else…if statements.

Syntax:

switch (expression) {
   case condition 1: statement(s)
   break;
   
   case condition 2: statement(s)
   break;
   ...
   ...
   ...
   
   case condition n: statement(s)
   break;
   
   default: statement(s)
}

Working Of Switch-case Statement:

Example:

let day = "monday"

switch (day) {
    case "sunday": 
        console.log("It is Sunday today.");
        break;
    case "monday": 
        console.log("It is Monday today.");
        break;
    case "tuesday": 
        console.log("It is Tuesday today.");
        break;
    case "wednesday": 
        console.log("It is Wednesday today.");
        break;
    case "thursday": 
        console.log("It is Thursday today.");
        break;
    case "friday": 
        console.log("It is Friday today.");
        break;
    case "saturday": 
        console.log("It is Saturday today.");
        break;
    default: 
        console.log("It seems your day is not in Calender.")
}

/* output:
It is Monday today.
*/

Loop:

for loop:

• “ for ”loop is used when the block of code is expected to execute for a specific number of times.

Example:

// print number from 1 to 10
for(let i = 1; i <= 10; i++){
    console.log(i);
}

/* output:   
1
2
3
4
5
6
7
8
9
10
*/

While loop:

• ‘while’ loop is used when the block of code is to be executed as long as the specified condition is true.

example:

// print 1 to 10 
let num = 1;  // intialization

while(num <= 10 ){  // condition
    console.log(num);
    num++;         // increment (Update statement)
}

/* output:   
1
2
3
4
5
6
7
8
9
10
*/

Do while:

• ‘do-while’ is a variant of ‘while’ loop.
• This will execute a block of code once before checking any condition.

// print 1 to 10
let num = 1; // intialization
do{
    console.log(num);
    num++;           // update statement
}while(num <= 10);  // condition