Primitive data types in Javascript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable with a string value.

Javascript

let greeting = [1];

Drag options to blanks, or click blank then click option'

A123

BHello

C"Hello"

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to use quotes for string values.

Using a number or boolean without quotes.

The value assigned to a string variable must be enclosed in quotes.

2fill in blank

medium

Complete the code to declare a variable with a boolean value.

Javascript

const isActive = [1];

Drag options to blanks, or click blank then click option'

Atrue

B"true"

C1

DFalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around true or false.

Using capitalized False instead of lowercase false.

Boolean values are true or false without quotes.

3fill in blank

hard

Fix the error in the code to correctly assign a number.

Javascript

let age = [1];

Drag options to blanks, or click blank then click option'

A"25"

Btwentyfive

Ctrue

D25

Attempts:

3 left

💡 Hint

Common Mistakes

Putting numbers inside quotes making them strings.

Using words instead of digits for numbers.

Numbers are written without quotes in JavaScript.

4fill in blank

hard

Fill both blanks to create an object with a string and a number property.

Javascript

const person = { name: [1], age: [2] };

Drag options to blanks, or click blank then click option'

A"Alice"

B30

Ctrue

DAlice

Attempts:

3 left

💡 Hint

Common Mistakes

Using unquoted strings for name.

Putting numbers in quotes for age.

The name property needs a string with quotes, and age needs a number without quotes.

5fill in blank

hard

Fill all three blanks to create a variable with undefined, null, and symbol values.

Javascript

let a = [1];
let b = [2];
let c = [3]('id');

Drag options to blanks, or click blank then click option'

Aundefined

Bnull

CSymbol

Dsymbol

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around undefined or null.

Using lowercase symbol instead of Symbol.

undefined and null are primitive values, and Symbol is a function to create unique symbols.

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