Declaring variables

In JavaScript, variables are essential because they allow developers to store, retrieve, and manipulate data efficiently. Imagine variables as labeled containers that hold various types of data, such as numbers, strings, or objects. This capability is foundational for developing dynamic and interactive web applications. In this topic, we will explore how to declare variables.

What is a variable?

A variable is a designated space in memory where data can be stored, accessed, and manipulated. Think of a variable as a box with a label, allowing you to identify and retrieve its contents when needed. Each variable has a unique name, which distinguishes it from others.

How to declare a variable?

Before using a variable, you should declare it, which means creating it and optionally assigning it a value. JavaScript provides two modern keywords for declaring variables:

• let defines a mutable variable, whose value you can change.

• const declares a constant variable, which prevents value overwriting.

When declaring a variable, name it appropriately. Assign a name that describes its contents. Choose meaningful and readable names for variables to make your code easy to understand.

Mutable variables

Let's create a mutable variable and explore why it's called mutable. Let's name it month and assign data to it using the = symbol:

let month = "November"; // declare the variable and assign it a value

In JavaScript, variables store any type of data. Here, you've stored the string November. You can access this string using the variable name:

let month = "November";
console.log(month); // outputs the content of the variable to the console

This code displays the variable's content in the console. In our case, the result will be the string November. Try it out yourself.

Now, let's try to change the variable and print its new value to the console:

let month = "November";
month = "December";

console.log(month); // December

Notice how the variable's value has changed. It now holds the string December.

Constants

Using const, we can declare immutable variables. For example, we can declare the immutable variable language and assign it the string JavaScript as its value:

const language = "JavaScript";

If we wanted to change the value of a variable created with the const keyword, we would get an error:

const language = "JavaScript";
language = "PHP"; // error

With this understanding of variables, you can build more complex and engaging programs.

Other ways to declare variables

In older scripts, you may notice that the keyword var is used instead of let. This keyword served to declare variables before let and const were introduced in the ECMAScript 6 (ES6) standard. Its syntax looks like this:

var age = 21;

Variables declared with let or const are limited to the block where they are defined. In contrast, variables declared with var are accessible throughout the entire function, even outside the block where they are declared. This can cause unintended variable pollution. Additionally, variables declared with var can lead to variable hoisting and potential bugs or errors due to accidental redeclaration. Therefore, it's advisable to use let or const in modern JavaScript for more predictable behavior.

You can also find code where variables are declared without keywords:

age = 21;

This is not good practice, either.

Best Practices

• Use const by default to declare variables. Switch to let only when you need to reassign the variable's value.

• Avoid using var, as it can lead to unexpected behavior due to its function scope and hoisting characteristics.

• Refrain from declaring variables without keywords, as this can inadvertently create global variables and lead to potential conflicts.

Conclusion

Variables are a fundamental concept in programming, allowing developers to store and manipulate data in an organized way. With variables, it is possible to create more complex and exciting programs. Remember to choose meaningful and readable names for your variables to make your code easy to understand. Ensure you use the correct syntax to declare variables as mutable (let) or immutable (const), as each type has its unique characteristics. By mastering variables, you will be one step closer to becoming a proficient programmer.