JAVASCRIPT :-

• Javascript is used for building logics of a web page.
• javascript is a high level programming language, used in both client side as well as server side.
• javascript comes from echma script so we see the latest version of javascript in the form of echma script.
• Now we used javascript version 6 i.e ES6 (echma script 6)
• In another way we called ES6 as the vanilla Javascript.
• Node JS is the run time environment of javascript.

Variable :-

• variable is a container to store some data.
• in javascript there are 3 types of variable are there...

1. var :-

• var is a type of variable which is used for changing the variable in later stage.
• var is used in oldest browser so now a days we are don't use var most of the cases.

2. let :-

• let is a type of variable which is also used for changing the variable in later stage.
• Now these days, most of the cases we used let for changing the variable.
• let is a block scope code so we have been used let in most cases.

3. const :- const means constant.

Rules for creating variable name :-

• variables names are case sensative "a" & "A" is different.
• Only letter, digits, underscore & special character is allowed. (do not keep white space over here).
• only letter, underscore or special character should be the 1st character only.
• reserved words cannot be a variable name. ex. for, while, var , let, this, boolean etc...

Datatype in Javascript :-

• datatypes is an attributes associated with a peice of data that tells a computer system how to interprit its value.
• in datatype we used "typeof" operator to know what type of data it is.
• mainlly in javascript there are 2 type of datatypes are there.

1. primitive Datatype :-

• in javascript there are 7 types of primitive datatypes are there like..

1. Number - Numbera re the type of datatypes those it contains some numerical values

2. Boolean - in boolean datatype we got boolean value like true/false

3. Undefiend - data is not define

4. Null - in this datatype we got null for the value means nothing

5. bigInt - in bigint we will get the big integer value (-999999999 to +999999999) on the above.

6. String - string is a type of datatype that can hold some character like names or words etc..

7. Symbol - in symbol we got one symbol of more than one value.

8. Reference Datatype

• reference datatypes are the type of datatype which can hold multiple element in a single frame.
• reference datatypes are -> array, object, function

1. Array :-

• Array is a coolection of similar type of datatype which can hold contigious memory location.
• array indexing start from "0".

ex. let arr = ["hari", "sita", "ram"] 0 1 2

2. Object :-

• object is a reference type of datatype where we can store more then one element is a single frame.
• mainly object are working on (key:value) pair.

ex:-

let hari = { "name" : "hari bandu sahoo", "phone no" : 56789032, "address" : "bhubaneswar", "carrier" : "good" }

• in the above example left side element are the keys & right side elements are the values of that key.

3. Function :-

• in function, we repeatedlly do the task in a function.
• function reduce our code complexity and time & space complexity.
• syntax :-

function ->

function my_schedule(){ console.log("we wake up at 6 am"); console.log("we go for a morning walk") }

function calling ->

my_schedule();

Operator in JS :-

• operator are the key features to do some task or operate some task.
• ex. A + B
• in the above example A & B are the operands, "+" is our operator.
• in javascript, there are 5 types of operator re there..

1. Arithmetic operator -> (+,-,*,/), %(modulus), ** (exponent)
2. Assignment Operator -> (=,+=,-+,*=,/=,%=,**=)
3. compairision operator -> (==, !==, ===)
4. Logical operator -> Logical AND (&&), Logical OR (||), Logical NOT (!)
5. unary operator -> increament (++), decreament (--)

logical AND (&&)

A B AND(&&)

T T T T F F F T F F F F

Logical OR (||)

A B OR(||)

T T T T F T F T T F F F

conditional statement :-

• to implement some condition in the code.
• there are 3 types of conditional statements are there

1. if condition :-

• if condition is true then statement is true.
• syntax :- if (condition){ statement }

2. if-else condition :-

• if condition is true then sttement is true otherwise false.
• syntax :- if (condition){ statement } else { statement }

3. if-elif condition or switch condition

• its check the comdition multiple times, where the condition is true, it returns the statement.

• if else if case. else condition if the default condition so if the condition doesn't satisfy any of the case then he print the default condition.

• syntax :- if (condition){ statement } else if(condition){ statement } else if(condition){ statement } else { statement }

practice task :-

write a code which can give grades to student according to their score.

1. 80-100 (A)
2. 70-79 (B)
3. 60-69 (C)
4. 50-59 (D)
5. 0-49 (fail - go for aganwadi)

Loops in Javascript :-

• loop are used to execute a piece of code again & again.
• there are 5 types of loop are there..

1. For Loop :-

• syntax :- for (initialization; condition; updation){ statement } ex. - we want to print "web Bocket" 5 times,

for (let i = 1; i <= 5; i++){ console.log("Web Bocket) }

working :-

i = 1 -> web bocket i = 2 -> web Bocket i = 3 -> Web Bocket i = 4 -> Web Bocket i = 5 -> Web Bocket

2. While Loop :-

• syntax :-

initialize; while (condition){ statement; update; }

ex -> Print "GIFT" 5 times.. in while loop

let i = 1 while (i <= 5){ console.log("GIFT"); i++; }

3. Do-While Loop :-

• syntax :-

initialize; do { statement; updation; } while (condition)

4. For-Of Loop :- it iterates on string & Array
5. For-In Loop :- it iterate on objects

String in Javascript :-

• Basically String is a sequence of character used to represent text.
• create a string -> let str = "web bocket".
• we calculate the string length -> str.length property.
• we calculate the string index -> str[0], str[1] ...etc

String Literals :-

• its a way to have embedded expression in string.
• its denoted by symbol ``.

String Interpolation :-

• to create string by doing substitution of placeholder.
• ex. -> string text ${expression} string text.

Escape symbol in String :-

1. \n -> new line
2. \t -> new tab

String Method in Javascript :-

1. str.toUpperCase()
2. str.toLowerCase()
3. str.trim()
4. str.slice(start,(end-1))
5. str1.concat(str2)
6. str.replace(oldVal, newVal) -> its checnge the 1st sequence
7. str.replaceAll(oldVal, newVal) -> its change all the old value
8. str.charAt(idx)

Array in Javascript :-

• Array is a collection of items.
• ex. let heros = ["iron man", "bat man", "spyder man"]
• array index starts from "0".
• arr[0], arr[1] ....etc

looping over an Array :-

• loop -> iteration
• syntax -> for (let i = 0; i < arr.length; i++){ statement }

practice question :-

1. for a given array with marks of students -> [89,76,45,90,38,93]. find the average marks of the entire class.
2. for a given array with price of 5 items -> [768,987,456,765,345]. all items have an offer of 10% off of them. change the array to store final price after applying offer.

Array methods on javascript :-

1. push - add an element to the end
2. pop - remove from the end
3. toString - convert array to string
4. concat - join multiple array and return one result
5. unshift - add an element to the start
6. shift - remove an element to the first
7. slice() - return a piece of the array
8. splice() - change original array (add, remove, replace)

Function in Javascript :-

• it is a block of code that perform a specific task, can be invoked(called) whenever we need.
• ex. (in-build function)

1. console.log("hello world") -> in that code log() is a function
2. "abc".toUpperCase() -> in this code toUpperCase() is a function
3. [1,2,3].push(4) -> in this code push() is a function.

• there are two types of function in javascript.

1. Normal Function :-

-> Type A function // function creation function functionName(){ // do some task }

// function calling functionName()

-> Type B function // function creation function functionName(parameter){ // do some task }

// function calling functionName(arguments)

2. Arrow Function :-

• Its a compact way of writing a function.
• it uses map function to retrive the backend data, filter function for filterise our data...

// function creation const functionName = (parameter..) => { // do some task }

// function calling fuctionName()

Normal function ->
function sum(a,b){ return a + b; } sum(2,3);

Arrow Function -> const sum = (a,b) => { return a + b; } sum(2,3);

practice task :-

1. create a function using the "function" keyword that takes a string as an argument & returns the number of vowels in that string. (TCS Interview Question)

For Each Loop in Array :-

• arr.forEach(callBackFunction)
• callBackFunction :- it is a function to execute for each element in the array.
• a callback is a function passed as an argument to another function.

ex. arr.forEach((val) => { console.log(val) })

practice task :-

1. create a function that reverse an array.
2. create a function that filter out negative numbers.
3. check if a string is a palindrome or not.

Map Method :-

• create a new array with the result of some operation. The value its callback returns are used to form a new array. Normally we create a new array by calling the function in every array element.
• map does not change the original array.
• it does not execute the function for empty array/element.
• syntax -> arr.map(callbackFnx (value,index,array))

ex. let newArr = arr.map((val) => { return val*2; })

Filter Method :-

• create a new array of element that gives true for a condition/filter.
• ex. all even element

let newArr = arr.filter((val) => { return val % 2 === 0; })