1. What is JavaScript?

4 min readNov 2, 2020


JavaScript is a dynamic computer programming language .it is lightweight and most commonly used as a part of web pages and it is the scripting & interpreted programming language.

2. Variable:

a variable used to store information ,that value can change in the computer program

if we want declare a variable we just remember 5 thinks first write the key word var or let or const and second give the name of variable third =sign fourth given variable value name and finally give semicolon ;

There are Three type of variable

  1. string type
  2. number type
  3. Boolean type
Example of variable type

if we want to know every variable which type we can identify easily

3. Mathematical operation in JavaScript

  1. (+)Addition
  2. (-)Subtraction
  3. ( *)Multiplication
  4. ( ** )Exponentiation (ES2016)
  5. ( / )Division
  6. ( % )Modulus (Remainder)
  7. ( ++ )Increment
  8. — Decrement

4 . Array

In JavaScript, array is a single variable that is used to store different elements.

how to declare array

var friendName=[“Amin”,“Tareq”,“Farhan”,“Sumon”,“Anik”,“Ashik”,“Babul”];

1 . at the beginning if we want to see the array value in ouput it’s very easy just use the array index like

console.log(friendeName [2]);

output will be : Farhan

2 . if we want to change value inside array we can write a simple way


console.log(friendeName );

output will be :[“Amin”,“Tareq”,“Farhan”,“Nabil”,“Anik”,“Ashik”,“Babul”]

Sumon will be change.

3. if we want to find out index or position in array

var position=friendName.indexof(“Babul”);


output will be :6

4. but if we write

var position=friendName.indexof(“Mamun”);

which is not define in array output will be -1 because it’s not include in array


output will be :-1

5 .Array value add in last

just write


output will be :[“Amin”,“Tareq”,“Farhan”,“Nabil”,“Anik”,“Ashik”,“Babul”,“Babul”,“Anika”];

6 .Array value add in first

just write


output will be :[ “Foysal”,“Amin”,“Tareq”,“Farhan”,“Nabil”,“Anik”,“Ashik”,“Babul”,“Babul”,“Anika”];

7 . Array value Delete at beginning


output will be :[“Amin”,“Tareq”,“Farhan”,“Nabil”,“Anik”,“Ashik”,“Babul”,“Babul”,“Anika”];

Foysal gone

8. In array also do slice

var number=[10,11,12,13,14,15,16];

var part1=number.slice(3,5);

output well be : [13,14];

remember that in using slice main array do not change.

9. In array also do splice

remember that in using slice main array will be change.

5 .Loop in JavaScript

1.why use loop

same think do again and again that’s why use loop

2. In JavaScript loop two type mostly use

  1. for loop
  2. while loop

for loop

for (variable declaration ;condition ; increment/decrement){



example :

var text = “”;
var i;
for (i = 0; i < 5; i++) {
text += “The number is “ + i + “<br>”;

while loop

while (condition) {
// code block to be executed

example :

while (i < 10) {
text += “The number is “ + i;

6 . Function

in JavaScript most useful and important thinks is function.

  1. What is function

function is a set of statement group of reusable code which can be called anywhere in your program.

Example of function:

function add(num1,num2){

var result=num1+num2;

return result;


var sum=add(10,20);


output will be : 30

num1 & num2 is a function parameter

and return is a keyword it’s duty is stop this statement

2.What is different between loop and function

  1. loop give output continuously do not stop give all the output until condition fulfil
  2. but function do not do this when user want this place show output it given anywhere user it call

8 . Factorial using function

function factorial(n){

var factorial =1;

for(var i=1;i<n; i++){



return factorial;


var result=factorial(10);


output will be :3628800

9. var/let/const


  1. it al time can use

2. var is a function scope inside the function area it can call



var myVariable=“This is var”;




  1. if have possibility to change the variable name then use the let l

example :

let patient=20;



let letVariable=“this is let”;



2. let is block scope it only work in block area not other


1 .if variable value do not have to chance to change in next that time use the


2. const fix no change


const country=“Bangladesh”;


10. Object in JavaScript

  1. What is object?

object is a collection of properties or method and property is an association between a name(or key) and a value

2.object declaration

var student1={name:“Babul”,id:18103045, phone:01725488};

var student2={name:“Kamrul”,id:19103045, phone:01925488};

console.log( student1);

{name:“Babul”,id:18103045, phone:01725488}

console.log( student2);

{name:“Kamrul”,id:19103045, phone:01925488}

3. if anybody wants to see only phone number

var phoneNo=student1.phone;

output :01725488;

4.if anybody wants change to phone number


output:{name:“Babul”,id:18103045, phone:0162015}