What are variables in javascript?

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By ecde.info

What are variables in javascript?

Photo of author

By ecde.info

Variables in programming are named storage locations in the computer’s memory that hold values. These values can be of various data types, such as numbers, text (strings), arrays, objects, and more. Variables are fundamental to most programming languages, including JavaScript, as they allow programmers to store, manipulate, and retrieve data throughout their code. The value of a variable can be changed as the program runs, which offers flexibility and dynamic control over the program’s behavior.

Declaring Variables in JavaScript

In JavaScript, variables can be declared using three keywords: var, let, or const.

  • var is the oldest keyword used to declare variables, but it has some scope limitations and peculiarities that can lead to bugs.
  • let was introduced in ES6 (ECMAScript 2015) and allows you to declare block-scoped variables, meaning the variable is limited to the block (denoted by curly braces {}) in which it is defined.
  • const is also block-scoped but is used to declare variables whose values are not intended to change throughout the script execution.

Examples of Variables

Here are five examples illustrating how variables can be used in JavaScript, showcasing different data types and declaration methods:

Example 1: Storing a Number

let age = 25;
console.log(age); // Outputs: 25

In this example, age is a variable that stores a number. We can use this variable to represent a person’s age in a program.

Example 2: Storing a String

const name = "Alice";
console.log(name); // Outputs: Alice

Here, name is a variable that holds a string value, which can be used to represent a person’s name.

Example 3: Storing an Array

let colors = ["Red", "Green", "Blue"];
console.log(colors[0]); // Outputs: Red

colors is a variable that stores an array of strings. Each element in the array represents a color.

Example 4: Storing an Object

const person = {
    firstName: "John",
    lastName: "Doe",
    age: 30
console.log(person.firstName); // Outputs: John

In this example, person is a variable that holds an object. This object represents a person with properties for their first name, last name, and age.

Example 5: Storing a Boolean

let isAdult = true;
if (isAdult) {
    console.log("Is an adult.");
} else {
    console.log("Is not an adult.");
// Outputs: Is an adult.

isAdult is a variable that stores a boolean value (true or false). This example uses the variable to determine if someone is considered an adult.

Importance of Variables

Variables are essential in programming for several reasons:

  • Reusability: Once a variable is defined, it can be reused multiple times throughout your program.
  • Readability: Using descriptive variable names makes your code easier to read and understand.
  • Flexibility: Variables allow you to write flexible and dynamic code where values can be changed and manipulated as needed based on user input or other conditions.

Example 6: Manipulating Numbers

let basePrice = 100;
let taxRate = 0.05;
let taxAmount = basePrice * taxRate;
let totalPrice = basePrice + taxAmount;

console.log("Total Price:", totalPrice); // Outputs: "Total Price: 105"

This example calculates the total price of an item by adding tax to the base price. Variables are used to store the base price, tax rate, the calculated tax amount, and the total price.

Example 7: Concatenating Strings

const firstName = "Jane";
const lastName = "Doe";
const fullName = firstName + " " + lastName;

console.log("Full Name:", fullName); // Outputs: "Full Name: Jane Doe"

Here, two string variables (firstName and lastName) are concatenated to form a full name. A new variable, fullName, stores the result of this concatenation.

Example 8: Boolean Logic

let lightOn = true;
let lightOff = !lightOn; // Logical NOT operation

console.log("Is the light off?", lightOff); // Outputs: "Is the light off? true"

In this scenario, the lightOn variable stores a boolean value indicating whether the light is on. The lightOff variable uses the logical NOT operator (!) to store the opposite value.

Example 9: Arrays and Loops

let fruits = ["Apple", "Banana", "Cherry"];
for (let i = 0; i < fruits.length; i++) {
    console.log("Fruit:", fruits[i]);
// Outputs: "Fruit: Apple", "Fruit: Banana", "Fruit: Cherry"

This example demonstrates an array storing a list of fruits. A for loop iterates over the array, and the loop variable i is used to access and print each element.

Example 10: Objects and Property Access

let book = {
    title: "The Great Gatsby",
    author: "F. Scott Fitzgerald",
    publishedYear: 1925

console.log("Book:", book.title, "by", book.author); // Outputs: "Book: The Great Gatsby by F. Scott Fitzgerald"

book is a variable holding an object that represents a book. The object has properties for the book’s title, author, and year of publication. Properties are accessed using dot notation.


These examples showcase how variables in JavaScript can be utilized to store different types of data—numbers, strings, booleans, arrays, and objects—and how they can be used in various operations, including arithmetic calculations, string manipulation, boolean logic, loops, and object property access. Understanding and mastering the use of variables is crucial for effective programming, as it allows developers to write flexible, dynamic, and readable code.

Understanding how to effectively use variables is a fundamental skill for any programmer, as they serve as the building blocks for constructing logical and functional code.

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