JavaScript.txt

script tag must be loaded in last, as it won't recognize the body tag, if defined earlier than it.
*************************************************************************

Javascript is a dynamically types language. We do not have to tell the datatype of a variable.
for e.g. if we are working in python while initializing the variable we have to define its datatype. Whereas, in JS there is no such thing.

e.g. fullName= "Abiha"
fullName= 25
console.log(fullName)
output---> 25 (dynamic nature allows string and int to be stores in a single variable)

LET, CONST AND VAR:
var: variable can be re declared & updated. A global scope variable. (not recommended)(creates confusion and errors, as it allows 
redefining the variable which is not a recommended way such as: var age= 29; var age= 58;)

let: variable can not be re declared but can be updated. A block scope variable. (e.g. let age= 29, age= 18) (value is updated in the
same variable but the variable is not declared again)

const: variable can not be re declared or updated. A block scope variable.

*************************************************************************
DATATYPES (TWO TYPES)

PRIMITIVE (7)
number
float
string
boolean
null  //object (absence of an object)
BigInt
Symbol

NON- PRIMITIVE (OBJECTS)
Arrays
Functions


HOW ARE WE ABLE TO MODIFY NAME or AGE OF Students when the object is declared as const????????
Since Student is an obj we can change the values for its keys, as  for displaying error here compiler 
needs to reference the memory address. 
That is why we are able to change the values of const objects, but not const variables.

*************************************************************************
LOOPS & STRINGS

TEMPLATE LITERALS 
just a string with back ticks. Helps in string interpolation. 
used to evaluate and embed expressions dynamically in template literals. 
const name = 'John Doe'; const age = 20; // Using template literals for string interpolation 
console. log(`My name is ${name} and I'm ${age} years old.
*************************************************************************
ARRAYS



DIFF BTW FOREACH() AND MAP
FOREACH---> doesnot return an array
MAP---> returns an array

FOREACH
let arr = [1, 2, 3];
arr.forEach((val) => {
  console.log(val + 1);
});

MAP
let output = arr.map((val) => val + 1);
console.log(output);
*************************************************************************
FUNCTIONS AND METHODS

DIFFERENCE
Functions are not defined for specific datatype and are generalized. Whereas,
methods are datatype specific. for e.g. toUpperCase() is a method which will only operate on string datatype.

*************************************************************************
WHY SHOULD WE WRITE JS IN SEPARATE FILE?
improve readibility
improve modularity 
helps in browser caching

WINDOW OBJECT
represents an open window in a browser.
global object that contains methods and properties.
automatically created by browser.
browser object (not JS object)
all code renders in window object.

DOCUMENT OBJECT MODEL
-when web page is loaded, the browser creates a DOM of the page.
-to access the HTML elements in JS
-the HTML elements are converted to objects in JS which are called as document avaible in out window object. window.document

window--> document (model of HTML code) ---> DOM ---> tree like structure --> individual elements boxes are called nodes (objects)

*************************************************************************
EVENTS
The change in state of an object is called event.
Events are fired to notify code of interesting changes that may impact code execution.

INLINE EVENT HANDLING
HTML ky through events define krna

if we have handeled events using inline and JS methods both. The priority will be given to the JS Event Handling.

*************************************************************************
CLASSES AND OBJECTS