Primitive data types in Javascript - Mini Project: Build & Apply

Understanding Primitive Data Types in JavaScript

📖 Scenario: You are learning how to store simple pieces of information in JavaScript. These simple pieces are called primitive data types. They include numbers, text, true/false values, and more.

🎯 Goal: You will create variables using different primitive data types and then display their values.

📋 What You'll Learn

Create variables with exact names and values for each primitive type

Use correct JavaScript syntax for each data type

Print the values of all variables exactly as specified

💡 Why This Matters

🌍 Real World

Primitive data types are the basic building blocks to store simple information like age, names, or true/false answers in any program.

💼 Career

Understanding primitive data types is essential for all programming jobs because they are used everywhere to hold and manipulate data.

1

Create variables with number and string types

Create a variable called age and set it to the number 25. Then create a variable called name and set it to the string "Alice".

Javascript

// Create a variable called age and set it to 25
// Create a variable called name and set it to "Alice"

Hint

Use let to create variables. Numbers are written without quotes. Strings need quotes like double quotes.

2

Add boolean and undefined variables

Add a variable called isStudent and set it to the boolean value true. Also add a variable called middleName and set it to undefined.

Javascript

let age = 25;
let name = "Alice";
// Add a variable isStudent set to true
// Add a variable middleName set to undefined

Hint

Boolean values are true or false without quotes. undefined means no value assigned.

3

Add null and symbol variables

Add a variable called car and set it to null. Then add a variable called id and set it to a new symbol with description "id".

Javascript

let age = 25;
let name = "Alice";
let isStudent = true;
let middleName = undefined;
// Add a variable car set to null
// Add a variable id set to Symbol("id")

Hint

null means empty value. Symbols are unique identifiers created with Symbol().

4

Print all variable values

Use console.log to print the values of age, name, isStudent, middleName, car, and id in that order, each on its own line.

Javascript

let age = 25;
let name = "Alice";
let isStudent = true;
let middleName = undefined;
let car = null;
let id = Symbol("id");
// Print all variables using console.log, each on a new line

Hint

Use console.log(variableName); to print each variable on its own line.

Practice

1. Which of the following is NOT a primitive data type in JavaScript?

easy

A. object

B. boolean

C. string

D. number

Solution

1. Step 1: Recall JavaScript primitive types

   JavaScript primitive types include string, number, boolean, undefined, null, symbol, and bigint.

2. Step 2: Identify non-primitive types

   Object is not a primitive type; it is a complex data type used to store collections.

3. Final Answer:

   object -> Option A

4. Quick Check:

   Primitive types exclude objects [OK]

Hint: Remember: objects are NOT primitives, others are [OK]

Common Mistakes:

• Confusing object with primitive types
• Thinking null is an object
• Mixing symbol with object

2. Which of the following is the correct way to declare a variable with a string primitive in JavaScript?

easy

A. let name = John;

B. let name = 'John';

C. let name = "John;

D. let name = `John;

Solution

1. Step 1: Check string declaration syntax

   Strings must be enclosed in matching quotes: single ('') or double ("") or backticks (``).

2. Step 2: Validate each option

   let name = 'John'; uses single quotes correctly. let name = John; lacks quotes. Options C and D have unclosed quotes.

3. Final Answer:

   let name = 'John'; -> Option B

4. Quick Check:

   Strings need matching quotes [OK]

Hint: Strings always need matching quotes around text [OK]

Common Mistakes:

• Missing quotes around string
• Using mismatched quotes
• Forgetting semicolon (optional but good)

3. What will be the output of the following code?

console.log(typeof 123);
console.log(typeof 'hello');
console.log(typeof true);

medium

A. "number", "string", "boolean"

B. "Number", "String", "Boolean"

C. "num", "str", "bool"

D. "integer", "text", "bool"

Solution

1. Step 1: Understand typeof operator

   typeof returns the type of a value as a lowercase string like "number", "string", or "boolean".

2. Step 2: Check each console.log output

   typeof 123 is "number", typeof 'hello' is "string", typeof true is "boolean".

3. Final Answer:

   "number", "string", "boolean" -> Option A

4. Quick Check:

   typeof returns lowercase type names [OK]

Hint: typeof returns lowercase type names as strings [OK]

Common Mistakes:

• Capitalizing type names
• Using short forms like 'num'
• Confusing typeof output with values

4. Find the error in this code snippet:

let value = null;
console.log(typeof value);

medium

A. null is not a valid value

B. typeof null returns 'null'

C. typeof null returns 'object' which is confusing

D. No error, code works fine

Solution

1. Step 1: Understand typeof null behavior

   typeof null returns "object" due to a historical JavaScript bug.

2. Step 2: Identify confusion

   This is confusing because null is a primitive but typeof shows "object".

3. Final Answer:

   typeof null returns 'object' which is confusing -> Option C

4. Quick Check:

   typeof null is 'object' (quirk) [OK]

Hint: Remember typeof null is 'object' due to JavaScript quirk [OK]

Common Mistakes:

• Expecting 'null' from typeof
• Thinking null is an object
• Assuming code throws error

5. You want to store a very large integer number beyond the safe integer limit in JavaScript. Which primitive type should you use?

hard

A. number

B. symbol

C. string

D. bigint

Solution

1. Step 1: Understand number limits in JavaScript

   The number type can safely represent integers only up to 2^53 - 1.

2. Step 2: Identify type for large integers

   bigint is designed to store integers larger than the safe limit without losing precision.

3. Final Answer:

   bigint -> Option D

4. Quick Check:

   Use bigint for very large integers [OK]

Hint: Use bigint for integers larger than safe number limit [OK]

Common Mistakes:

• Using number for very large integers
• Using string instead of bigint
• Confusing symbol with number types