JavaScript-Learning

1. Basic JavaScript Syntax

Hello World in JS

console.log("Hello World");

OUTPUT

Hello World

• The log( ) function is used to print a value to the console.

Variables

• Variables in JS are used to store a value under a name.

Variable Declaration using 'var'

var name = "Avantika";
var age = 21;
console.log(name, age);

OUTPUT

Avantika 21

• 'var' was an older way of to create variables.
• It ignores the block scope.

Variable Declaration using 'let'

let name = "Avantika";
let age = 21;
console.log(name, age);

OUTPUT

Avantika 21

• 'let' works same as 'var'.

Variable Declaration using 'const'

const name = "Avantika";
const age = 21;
console.log(name, age);

OUTPUT

Avantika 21

• 'const' is also used to create variables.
• It doesn't allow updation of the variable once it is formed.

Data Types

Numbers

let age = 21;
let phone = 12345;
let pi = 3.14159;
console.log(age, phone, pi);

OUTPUT

21 12345 3.14159

• Number datatype in JS includes both integers and decimal numbers.

Strings

let name = "Avantika";
let country = "India";
console.log("My name is " + name + " and I live in " + country);

OUTPUT

My name is Avantika and I live in India

• String is a combination of characters. enclosed in double-quotes( " " ).

Arrays

let colors = ["red", "blue", "pink", "green"];
console.log(colors);

OUTPUT

["red" , "blue" , "pink" , "green"]

• Arrays are combination of multiple values of various data types under a single name.

Boolean

let is_rain = False;
let can_vote = True;
console.log(is_rain, can_vote);

OUTPUT

False True

• Boolean consists of only two values - True and False.

Null and undefined

let a;
let b = null;
console.log(a, b);

OUTPUT

undefined null

• Null - It represents the intentional absence of a value.
• Undefined - It shows that the value is yet to be assigned.

Comparison Operators

let age = 18;

console.log(age == 18); // Is equal to
console.log(age != 18); // Is not equal to
console.log(age > 18); // Is greater than
console.log(age < 18); // Is less than

OUTPUT

True
False
False
False

Loose comparison

let age = 18;
console.log(age == 18);
console.log(age == "18"); // Implicit type conversion takes place

OUTPUT

True
True

• Before comparing, Type conversion takes place.

Strict comparison

let age = 18;
console.log(age === 18);
console.log(age === "18"); // no type conversion takes place.

OUTPUT

True
False

• No type conversion takes place before comparison.

Type Conversion

Implicit conversion

let age = 18;
console.log(age == 18);
console.log(age == "18"); // Implicit type conversion takes place

OUTPUT

True
True

• In this example, type conversion is done by browser, thus it is an Implicit conversion.

Explicit conversion

let age = 20;
console.log(age);

age = "Twenty";
console.log(age);

OUTPUT

20
Twenty

• Type conversion done by the user is known as Explicit Type Conversion.