Real-Life Examples of Using JavaScript Variables and Data Types

📚 Quick Study Guide

• 💡 Variables: Containers for storing data values. Declared using `var`, `let`, or `const`.
• 🔑 Data Types: Categories of values that variables can hold.
• 🔢 Primitive Data Types:
  • 🧵 String: Textual data (e.g., "Hello").
  • #️⃣ Number: Numeric data (e.g., 10, 3.14).
  • boolean Boolean: True or false values.
  • null Null: Represents the intentional absence of a value.
  • undefined Undefined: Represents a variable that has been declared but not assigned a value.
  • symbol Symbol: Unique and immutable identifiers (ES6).
  • bigint BigInt: Used for integers of arbitrary length(ES2020).
• 🧱 Composite Data Types:
  • 📦 Object: A collection of key-value pairs.
  • array Array: An ordered list of values.
• ➕ Operators: Used to perform operations on variables and values (e.g., +, -, *, /).
• 🧮 Type Coercion: Automatic conversion of one data type to another.

Practice Quiz

1. What is the correct way to declare a variable named `userName` in JavaScript?
   1. var userName = "John";
   2. userName = "John";
   3. string userName = "John";
   4. const userName;
2. Which of the following is NOT a primitive data type in JavaScript?
   1. String
   2. Number
   3. Object
   4. Boolean
3. What will be the output of `console.log(typeof null);`?
   1. "null"
   2. "object"
   3. "undefined"
   4. "Null"
4. Which operator is used for strict equality comparison in JavaScript?
   1. ==
   2. =
   3. ===
   4. !=
5. What data type is most appropriate for storing a list of student names?
   1. String
   2. Object
   3. Array
   4. Number
6. If `let age = "25";`, what is the result of `age + 5`?
   1. 30
   2. "30"
   3. "255"
   4. Error
7. Which keyword is used to declare a constant variable in JavaScript?
   1. var
   2. let
   3. const
   4. static