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Hariharan S J
Hariharan S J

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Understanding JavaScript the Easy Way

History of JavaSript

1. The Birth of JavaScript (1995)

JavaScript was created by Brendan Eich in 1995 while he was working at Netscape.

  • Initially named Mocha
  • Later renamed to LiveScript
  • Finally renamed JavaScript (because Java was very popular at that time, and the name helped in marketing)

Interestingly, the first version of JavaScript was developed in just 10 days.

2. Standardization (1997)

In 1997, JavaScript was standardized by ECMA International under the name ECMAScript (ES).

This ensured that different browsers followed the same core rules and reduced compatibility issues.

Variables in javascript

Variables in JavaScript are used to store data values.
You can think of a variable as a container that holds information.

How to Declare Variables

In JavaScript, there are three ways to declare variables:

1.Var(Old Method)

`var name = "Hari";
`
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  • Function-scoped

  • Can be re-declared

  • Not recommended in modern JavaScript

2.let(Modern & Recommended)

`let age = 22;
`
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  • Block-scoped

  • Can be updated

  • Cannot be re-declared in the same scope

3.const(Constant Value)

`const country = "India";
`
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  • Block-scoped

  • Cannot be updated

  • Cannot be re-declared

Rules for Naming Variables

  • Must start with a letter, _, or $

  • Cannot start with a number

  • Case-sensitive (name and Name are different)

  • Avoid reserved keywords (like if, for, while)

Datatypes in javascript

In JavaScript, data types define the type of value a variable can hold
JavaScript has two main categories of data types:

1.Primitive Datatype
2. Non Primitive Datatype

1.Primitive Datatype

Primitive data types are basic data types that store a single value directly in memory
They are immutable, meaning their value cannot be changed once created (a new value is created instead).

1.Number

Represents both integers and decimal values.

`let age = 21;
let price = 105.234;
`
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2.String

Represents text (written inside quotes).

`let name = "Hari";
let message = 'Hello World';
`
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3.Boolean

Represents true or false values.

`let isLoggedIn = true;
let isAdmin = false;
`
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4.Undefined

A variable that is declared but not assigned a value.

`let x;
console.log(x); // undefined
`
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5.Null

Represents an intentional empty value.

`let data = null;

`
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6.BigInt

Used for very large numbers.

`let bigNumber = 123456789012345678901234567890n;
`
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7.Symbol

Used to create unique identifiers (mostly used in advanced concepts).

`let id = Symbol("unique");
`
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2.Non Primitive Datatype

Non-primitive data types (also called reference data types) store collections of values or complex data
They are stored as references (memory addresses) instead of storing the actual value directly

They are mutable, meaning their contents can be changed.

1.Object

Stores data in key–value pairs.

`let person = {
  name: "Hari",
  age: 21
};
`
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2.Array

Used to store multiple values in a single variable.

`let numbers = [1, 2, 3, 4];
`
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3.Function

Functions are also treated as objects in JavaScript.

`function greet() {
  console.log("Hello!");
}
`
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Top comments (1)

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sundarpichai_google_e303 profile image
Sundar Pichai google •

Awesome blog Very beginner-friendly explanation.
I have question:
Can you explain the difference between null and undefined in more detail?
How does JavaScript handle memory for primitive vs reference types?
Can you explain more about Symbol and where it is used in real applications?
Why are functions treated as objects in JavaScript?
What are some common mistakes beginners make while using var, let, and const?
Since JavaScript was created in 10 days, why is it so powerful today? What made it evolve so much?
What are the next important topics beginners should learn after variables and data types?
Can you write the next blog about scope and hoisting in detail?

EXPLAIN ALL QUESTION.