Javascript:
- JavaScript is a scripting language primarily used to create dynamic and interactive features on web pages.
- It works alongside HTML (for structure) and CSS (for styling) to enhance user experiences by enabling functionalities like animations, form validations, and real-time updates.
- JavaScript is a powerful and flexible programming language for the web that is widely used to make websites interactive and dynamic.
- JavaScript can also able to change or update HTML and CSS dynamically.
- JavaScript can also run on servers using tools like Node.js, allowing developers to build entire applications with it.
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History of Javascript:
- JavaScript was created in May 1995 by Brendan Eich, a developer at Netscape Communications Corporation.
- It was initially developed in just 10 days and was first named Mocha, later renamed LiveScript, and finally became JavaScript.
- It was first implemented in Netscape Navigator 2.0, one of the most popular web browsers of the time.
- In 1997, JavaScript was standardized as ECMAScript by the European Computer Manufacturers Association (ECMA) to ensure compatibility across different browsers.
- The first version of ECMAScript, ES1, was released in June 1997.
Reference:
History of JavaScript - GeeksforGeeks
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How Js Works?
- JavaScript is a single-threaded, event-driven language that runs in environments like browsers and Node.js.
- It executes code using a JavaScript engine (e.g., V8, SpiderMonkey) and manages asynchronous operations via the event loop.
VARIABLES IN JAVASCRIPT:
- In JavaScript, a variable is a container for storing data values.
- Variables are fundamental to programming as they allow you to store, manipulate, and retrieve data.
Rules for Naming Variables:
- Must start with a letter, underscore (_), or dollar sign ($).
- Can contain letters, numbers, underscores, or dollar signs.
- Case-sensitive (age and Age are different).
- Cannot be a JavaScript reserved keyword (e.g., let, class, return).
Declaring Variables:
1.Using var:
- The var keyword was traditionally used to declare variables in JavaScript.
- Variables declared with var are function-scoped and can be re-declared within the same scope without causing an error.
Scope:
Function-scoped (or globally scoped if declared outside a function).
Hoisting:
Hoisted to the top of the scope and initialized with undefined.
Redeclaration:
Allowed within the same scope.
syntax:
// var
var name = "Alice";
example:
var x = 10;
var x = 20; // Redeclaration allowed
console.log(x); // 20
2.Using let:
- The let keyword was introduced in ES6 (2015) and is block-scoped.
- This means that a variable declared with let is only accessible within the block it was declared in.
- Unlike var, let does not allow re-declaration within the same scope.
Scope:
- Block-scoped ({ ... }).
Hoisting:
- Hoisted but not initialized (Temporal Dead Zone until declared). Redeclaration:
- Not allowed in the same scope.
syntax:
// let
let age = 25;
example:
let y = 10;
// let y = 20; // ❌ Error: Cannot redeclare
y = 20; // ✅ Allowed
console.log(y); // 20
3.Using const:
- The const keyword is also block-scoped and is used to declare variables that should not be reassigned.
- However, the contents of objects and arrays declared with const can still be modified.
Scope:
- Block-scoped. Hoisting:
- Hoisted but not initialized (Temporal Dead Zone). Redeclaration:
- Not allowed. Reassignment:
- Not allowed (value is constant).
syntax:
// const
const country = "India";
example:
const z = 10;
// z = 20; // ❌ Error: Assignment to constant variable
console.log(z); // 10
Special Variable Types:
Global Variables:
Declared outside any function/block; accessible everywhere.
Local Variables:
Declared inside a function/block; accessible only there.
Static Variables:
Retain value between calls.(to be discussed)
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