Advance Concept of javaScript

masud howlader
3 min readMay 6, 2021

JavaScript is a powerful programing language. Nowadays knowledge about JavaScript is must necessary for being a good programmer or developer.

Today I will discuss some JavaScript Advance Concept.

Understanding of JS Primitive

Primitive values are numbers and strings among others things. There are 6 primitive types and an Object type.

1. Undefined

2. Null

3. Number

4. String

5. Boolean

6. Symbol


undefined is a property of the global object. That is, it is a variable in the global scope. The initial value undefined is the primitive value undefined.

function test(t) {

if (t === undefined) {

return ‘Undefined value!’;


return t;


let x;


// expected output: “Undefined value!”


The value null represents the intentional absence of any object value. It is one of JavaScript's primitive values and is treated as falsy for boolean operations.

typeof null === ‘object’ // true


There is only one number type. There is no specific type for integers. The number can be written with or without a decimal point. It is able to represent floating-point numbers, the number type has three symbolic values: +Infinity, -Infinity, and NaN (not-a-number).

var num1 = 10;
var num2 = 15.5;
var num3 = 20 / +0;
var num4 = 20 / -0;


A string in JavaScript is a sequence of characters. In JavaScript, strings can be created directly by placing the series of characters between double (“) or single (‘) quotes.

var str1 = “Hello, World!”;
var str2 = ‘Hi, Welcome to JavaScript Tutorial’;


It is logical a entity. A variable can have two values true or false.

var isActive = true;
var isDisabled = false;


New in ECMAScript6. A Symbol is a unique and immutable identifier.

var x = Symbol();
var y = Symbol(10);
var z = Symbol(‘Hello’);

Js Objects

In JavaScript, an object is a standalone entity, with properties and type. Compare it with a car, for example. A car is an object, with properties. It has a color, a design, weight, a material, it is made of, wheels, etc.

var myCar = {
make: ‘Ford’,
model: ‘Mustang’,
year: 1969

Js Functions

In JavaScript, a function allows you to define a block of code, give it a name and then execute it as many times as you want. A JavaScript function can be defined using a function keyword. I will discuss functions in detail and their parameters in a different article sometime.

Note: If you are writing several “helper” functions and the code that uses them, there are three ways to organize the functions.


function functionName(param) {
return param+ param;

JS Coding Style

Your code should be human readable, clean, well commented, meaningful naming for variables and functions and here I am giving some tips.