JavaScript Data Types and Variables

Anton Ioffe - July 31st 2023 - 2 minutes read

JavaScript Data Types and Variables

1. Introduction

In the world of programming, understanding data types and variables is fundamental. In JavaScript, these concepts form the bedrock upon which all scripts are built. In this post, we'll delve into what data types are, explore the diverse types available in JavaScript, and see how variables come into play.

2. Understanding Variables

At its core, a variable is like a label for a piece of data in your program. Imagine it as a container that holds information.

Declaration: In JavaScript, we historically used var to declare variables. However, with the advent of ES6, let and const have become the new standards.

var oldWay = "Using var";
let modernWay = "Using let";
const unchangingWay = "Using const";

Naming: Always remember to give your variables descriptive names, making your code easier to understand. Also, JavaScript uses camelCase by convention.

3. Primitive Data Types

Number: Both integers and floating-point numbers fall under this category. JavaScript has special numbers too: NaN (Not-a-Number), Infinity, and -Infinity.

let integer = 10;
let float = 10.5;
let notANumber = 0/0;  // Produces NaN

String: Textual data comes under this type.

let singleQuotes = 'Hello';
let doubleQuotes = "World";
let templateLiterals = `Hello, ${singleQuotes} ${doubleQuotes}!`;

Boolean: Represents truthy or falsy values - true or false.

Undefined and Null: These represent the absence of value. They are distinct, with undefined typically suggesting a variable has been declared but not assigned, while null means the value is intentionally set to no value.

Symbol & BigInt: Symbols ensure unique property keys, while BigInt allows representation of integers larger than 2^53.

4. Composite (Reference) Data Types

Object: A collection of properties. Each property has a key and a corresponding value.

let person = {
    name: "Alice",
    age: 25

Array: An ordered collection of values.

let fruits = ["apple", "banana", "cherry"];

Function: Remember, in JavaScript, functions are objects too!

function greet() {
    return "Hello, world!";

5. Special Data Types

Both NaN and Infinity are unique types in JavaScript. While NaN indicates an invalid number operation, Infinity represents an unbounded number value.

6. Type Coercion

JavaScript can be sneaky! It often converts types implicitly.

let result = '5' + 3;  // '53'

To understand a variable's type, use the typeof operator.

7. Conclusion

A robust grasp of data types and variables is critical for any aspiring JavaScript developer. They lay the foundation for more advanced topics. The more you understand them, the more confident and efficient you'll become in your coding journey.

8. Challenge/Exercise Section

  • Convert a string number to a real number and add 10 to it.
  • Declare an array and add a new item to its beginning.
  • Create an object representing a book with properties: title, author, and year.
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