Content

• JavaScript Numbers and Methods
• JavaScript Conditional Statements
• JavaScript Switch Statement
• Loops in JavaScript
• JavaScript Maps
• JavaScript Type Conversion

JavaScript Numbers and Methods

• JavaScript has only one type of number,numbers can be written with or without decimals.
• Unlike many other programming languages, JavaScript does not define different types of numbers, like integers, short, long, floating-point etc.

Example :

// A number with decimals
let x = 3.14;

// A number without decimals
let y = 3;

JavaScript Number Methods

• Number methods help you work with numbers.
• The toString() method returns a number as a string.
• toFixed() returns a string, with the number written with a specified number of decimals
• Number() can be used to convert JavaScript variables to numbers
• parseFloat() parses a string and returns a number. Spaces are allowed. Only the first number is returned
• NaN is a JavaScript reserved word indicating that a number is not a legal number.

Example : Number Methods

//toString()
let x = 123;
x.toString();

//toFixed()
let y = 9.656;
y.toFixed(2);

//Number()
Number("10");

//parseFloat()
parseFloat("10.33");

JavaScript Conditional Statements

• Conditional statements are used to perform different actions based on different conditions
• Very often when you write code, you want to perform different actions for different decisions
• You can use conditional statements in your code to do this
• if to specify a block of code to be executed, if a specified condition is true
• else to specify a block of code to be executed, if the same condition is false
• else if to specify a new condition to test, if the first condition is false
• switch to specify many alternative blocks of code to be executed

Example : JavaScript Conditional Statements

//if..else
let age = 25;
if( age > 18)
{
    console.log("My age is greater than 18");
}
else
{
    console.log("My age is less than or 18");
}

//if else ladder
let age = 25;
if( age > 30)
{
    console.log("My age is greater than 30");
}
else if(age >21)
{
    console.log("My age is greater than 21");
}
else
{
    console.log("My age is less than 18");
}

//Switch case
switch (new Date().getDay()) 
{
    case 6:
      text = "Today is Saturday";
      break;
    case 0:
      text = "Today is Sunday";
      break;
    default:
      text = "Looking forward to the Weekend";
  }

Loops in JavaScript

Loops are used when we want to repeat an action or run some code multiple times

• for Loop
• for…in Loop
• foreach Loop
• while Loop
• do…while Loop

for Loop

The for loop is used when we want to execute the set of statements for a certain number of times.

Example :

for(var j=1; j<=7; j++) 
{
console.log(j);
}
//check log in browser for output

---

for…in Loop

It is a special type of loop, used when we want to iterates over the properties of an object or the elements of an array.

Example :

var person = {name: "Shree", language: "JavaScript", age: 28};
for(var p in person) 
{  
console.log( p + " = " + person[p]); 
}

---

foreach Loop

With the help of forEach loop, we can execute a function on each item within an array.

Example :

const  evenno = [2,4,6,8,10];
evenno.forEach(showen);
 
function showen(item, index)
{
console.log(item);
}

---

while Loop

A while loop is used when we do not know how many times a certain block of code should execute.

Example :

let x = 1, y = 6;
while (x <= y) 
{
console.log(x);
x += 1;
}

---

do..While Loop

In this loop, the body inside the do statement is executed first,then the condition is evaluated.

Example :

let a = 1;
let b =3;
do {
console.log(a);
a++;
} while(a <= b);

JavaScript Maps

• A Map holds key-value pairs where the keys can be any datatype.
• A Map remembers the original insertion order of the keys.

Map Properties and Methods

Method	Description
new Map()	Creates a new Map
set()	Sets the value for a key in a Map
get()	Gets the value for a key in a Map
delete()	Removes a Map element specified by the key
has()	Returns true if a key exists in a Map
forEach()	Calls a function for each key/value pair in a Map
entries()	Returns an iterator with the [key, value] pairs in a Map
Property	Description
size	Returns the number of elements in a Map

Example :

// Create a Map
const fruits = new Map();
                        
// Set Map Values
fruits.set("apples", 500);
fruits.set("bananas", 300);
fruits.set("oranges", 200);

fruits.get("apples");    // Returns 500
fruits.size; //result - 3

JavaScript Type Conversion

• JavaScript variables can be converted to a new variable and another data type
• Converting Strings to Numbers
• Converting Numbers to Strings etc

Example

Number("3.14")    // returns 3.14
parseFloat("3.14") //returns 3.14

let x = 123;
x.toString(); // returns 123 as string