In this article, we are going to learn the followings:

• What a variable is in programming?
• Initializing a variable in few programming languages
• Working with variables in JavaScript

What is a variable in programming?

In programming, variables are a symbolic name that holds information or value stored and can reference a memory location. It can also manipulate the stored information in a computer program as well.

Amateur Scenario

Imagine a warehouse where we store goods and then wrap them in a box to stop them from spoiling. We place each of the goods into a box; We give the box a name (handle) and fit many goods into the box.

In the scenario above, the warehouse represents the storage. The goods represent the proposed store information; the box represents the variable, while the box name represents the variable's name, which can reference the variable's location in memory.

Initializing a variable in few programming languages

Many programming languages are out there, and they all support variables. They have their own ways of initializing them. For example, to declare a variable in Python, you will need to set the variable's name and assign it a value (data types).

Python Example:

programming_language = "Python"

The above snippet showed how we could declare a variable in Python and adhere to the definition we provided at the beginning of this article. We first set the variable name as programming_language, and then assigned it a value called Python.

We can also try initializing a variable in C. We will set the variable name and assign it a value.

C Example:

char programming_language = "C"

The above snippet showed how we could declare a variable in C and adhere to the definition we provided at the beginning of this article. We first set the variable data type as char and variable name as programming_language, and we then assigned it a C. 

Working with variables in JavaScript

Like those examples above, in JavaScript, we declare a variable by using the variable's keyword, then the name, and then assigning it a value. There are three fundamental ways in which we can declare a variable in JavaScript, and we do it by using the var, let, and const keywords.

Before EmacScript 2015 or ES6, we normally declare a variable using the var keyword.

Declaring variable using the var keyword

Example A

var name = "Carlos";

In Example A above, we declare a variable called name and assigned it a value called Carlos. In JavaScript, when declaring a variable, anything on the right-hand side gets assigned to the left-hand side through the assignment operator, which is the = or the equal sign. We can safely say we're assigning Carlos to the name variable with that knowledge.  Any variable declared using the var keyword gets added to the global scope, which basically means it is accessible to the window's object in the browser or the global's object in NodeJS. That means if you have the variable name being used in multiple blocks in your program, it gets cumbersome.

Example B:

var name = "Carlos";

if (name.length >= 4) {
 var name = "Rambo";
 console.log ("My name is " + name)
}

console.log ("My name is " + name)

In Example B, we have started with the first line by assigning the value Carlos to the variable's name, which we called name. I know the next block must be new to you if you're a beginner don't worry, we will get more details later. Basically, the next block sets a condition that states, "If the length of the variable name has 4 characters or more characters re-declared name and assign it a value Rambo in our case.".

Let's talk about const and let

For const and let, the same way we've declared variables using the var keyword also applies, but they don't follow the global scope. They're block scope, when using const it serves as a constant and you can't reassign or redeclare its variable's identifier.

For let it can be reassigned but can't be redeclared as we saw for var. Below are few examples of using let and and const.

Example C using const

const name = "Carlos";
console.log('My name is ', name) //outputs => My name is Carlos

name = "Paul" // Uncaught TypeError: invalid assignment to const 'name'

Let's talk about the above example, we started by first declaring a variable called name using the const keyword and assigned it a value Carlos as a string. On the next line, we then logged a string containing the const variable name which gave us => "My name is Carlos". Lastly, we decided to reassign the variable name to a string called Paul but got an Uncaught TypeError which states that reassigning the variable name to the string Paul is invalid. Like I said earlier you cannot reassign or redeclare a variable using const. Hope you remember that when dealing with variables using const.

Example D using let

let name  = "Carlos";
console.log('My name is ', name) //outputs => My name is Carlos

name = "Paul" // name is now Paul
console.log('My name is ', name) //outputs => My name is Paul

let name = "John" // Uncaught SyntaxError: redeclaration of let name

Let's talk about the example above, we started by declaring a variable name using let and assign it a string Carlos. Next, we logged a string containing the name variable which gave us => My name is Carlos. Next, we reassign the variable name to the string Paul with any error because it accepts reassigning. Now, name holds the string Paul. Next, we logged a string containing the name variable which gave us => My name is Paul. Lastly, we tried redeclaring name and assigning it a string John and got an error that redeclaring variable name will result in a SyntaxError.

Summary

We talked about variables in programming and how it stored information, we moved on to talk about declaring variables in different programming languages and explained how each works. We then move on to talk about variables in JavaScript and how we can declare, assign, reassign variables in JavaScript. Now that you know how variables in JavaScript works, I have a few suggestions for you.

Suggestions

• Don't you ever use var going forward, it is cool if you know what you're doing but yeah there are so many wats in JavaScript. So, to be on the safe side always don't use it.
• When you are starting a project in JavaScript and don't know if a variable is going to change or not, use const. In fact, always declare your variable using const, if its values will change then you use let.

Thanks, for reading through, I am open to any suggestion. Hope this helps you and will love to see some examples from you all in the comment below.