Cover image for [freeCodeCamp] Basic JavaScript – Comments, Variables and Mathematical Operations

[freeCodeCamp] Basic JavaScript – Comments, Variables and Mathematical Operations

gutsytechster profile image Prashant Sharma Originally published at gutsytechster.wordpress.com ・3 min read

Hello folks!

I have planned to complete the JavaScript curriculum from the freeCodeCamp. I have always wanted to complete a course on JavaScript but couldn't do so due to procrastination, laziness and a lot of other reasons.

But this time, I feel that not only learning but keeping a record of each concept and topic, will keep me motivated to continue the course and complete it until it ends. Another reason to choose the freeCodeCamp was to come across this playlist by Florin pop. He has done an amazing job there.

This will be a series of posts, which would include different topics, involved in the freeCodeCamp's JavaScript curriculum. Now, without any more delay, let's start with topics.


We can comment JavaScript code using // or /* */. Although both of them are valid comment specifiers. We use // for single-line comments and /* */(start with /* and end with */) for multi-line comments. For eg.

// Single Line or inline comment
   Line of 

Declaring and Initializing Variables

We know, that variables are used to store data. In JavaScript, we mainly have seven kinds of data types which are

  • undefined
  • null
  • boolean
  • string
  • symbol
  • number
  • object

JavaScript is also a dynamically typed language i.e. a variable in JavaScript can hold any type of value at any point of time within a program. We use the var keyword to declare variables in JavaScript as

var myName;

Here myName is a variable, which can store any data type from the above list. Also, don't forget to end a JavaScript statement with a semicolon(;).

Variables in JavaScript can contain numbers, letters, $, _ but can't contain spaces and start with numbers.

We can  as well assign a value to the variable using assignment = operator as

myName = "Prashant";

You can also initialize a variable at the time of its declaration as

var myNum = 7;
var anotherNum = myNum;

Quirks with uninitialized variables

  • When you don't initialize a variable, rather just only declare it, they hold the value undefined.
  • Performing any mathematical operation with undefined will result in NaN which means Not a Number.
  • Performing concatenation with undefined by adding a string literal to it will result in a string "undefined".

JavaScript is a case-sensitive language. It means variable myvar and myVar are different due to case insensitivity of letter v.  In JavaScript, the best practice to define variables is to define them in camelCase.

Mathematical Operations in JavaScript

Number data type is used to represent numeric data. There are various operators in JavaScript.

  • We can add two numbers in JavaScript using + operator as
var a = 10 + 10; // assigned 20
  • We can subtract two numbers in JavaScript using - operator as
var b = 15 - 5; // assigned 10
  • We can multiply two numbers using * operator as
var c = 5 * 10; // assigned 50
  • We can divide two numbers using / operator as
var d = 80 / 10; // assigned 8

Until now, we have just used some basic mathematical operation which we've seen already in mathematics. However, there are some other helpful mathematical operators like

  • Increment a number by 1 using ++ operator. Yes, I hear, you say this can easily be done as
var = var + 1;

However, JavaScript provides a shorthand to achieve it without the need of an assignment operator. The above statement is equivalent to

  • Decrement a number by 1 using -- operator. Similarly, as the increment operator, we can decrement a numerical value stored in a variable in a concise way as

Some other operations are

  • You can create Decimal numbers by just assigning the variable to the floating value. For e.g.
var pi = 3.14;

is a valid decimal number. All other arithmetic operations described above can also be performed with decimal numbers. :)

  • We have remainder operator i.e. % in JavaScript to find the remainder of a division. For e.g.
var rem = 7 % 3;  // assigned 1

This operation is widely used for finding out even and odd numbers as a number properly divisible by 2 would be called as even, and odd otherwise.

JavaScript provides some shorthand for compound assignments for various mathematical operations like, +=, -=, *=, /= etc.  You can use them as

var a = 1;
a += 5;  // a = a + 5

Other shorthand operators work in the same fashion.


In this post, we've got familiar with concepts like comments, variables and various mathematical operations in JavaScript.


Let's meet in the next post, covering some other JavaScript fundamentals. Till then, be curious and keep learning! :)

Posted on by:

gutsytechster profile

Prashant Sharma


Hey everyone! I am an open source enthusiast who loves to code. I am an aspiring Full stack developer. My weapon of code is Python and I enjoy creating REST APIs through Django REST Framework.


markdown guide