Type checking using typeof in Javascript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check the type of variable value.

Javascript

console.log(typeof [1]);

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

Avalue

B"value"

Ctypeof value

Dtypeof

Attempts:

3 left

💡 Hint

Common Mistakes

Putting the variable name inside quotes, which makes it a string literal.

Using typeof inside typeof like a function call.

The typeof operator returns the type of the variable. You need to pass the variable name value to it.

2fill in blank

medium

Complete the code to check if input is a string.

Javascript

if (typeof input === [1]) {
  console.log("It's a string!");
}

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

Astring

B"string"

C'string'

D"String"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the type name without quotes, causing a ReferenceError.

Using uppercase letters in the type string.

The typeof operator returns a string describing the type, so you must compare it to the string "string" (all lowercase).

3fill in blank

hard

Fix the error in the code to correctly check if num is a number.

Javascript

if (typeof num === [1]) {
  console.log("It's a number!");
}

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

A"number"

B== "number"

C=== "number"

D"Number"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a single equals sign = instead of ===.

Using uppercase letters in the type string.

Use the strict equality operator === to compare the result of typeof with the string "number". The original code used a single equals sign =, which is an assignment, not a comparison.

4fill in blank

hard

Fill both blanks to create an object with keys as variable names and values as their types.

Javascript

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

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

Atypeof name

Btypeof age

C"string"

D"number"

Attempts:

3 left

💡 Hint

Common Mistakes

Putting quotes around the typeof expressions, making them strings.

Using the type strings directly instead of typeof expressions.

To get the type of variables name and age, use typeof name and typeof age respectively.

5fill in blank

hard

Fill all three blanks to create a function that returns true if val is a boolean.

Javascript

function isBoolean(val) {
  return typeof [1] [2] [3];
}

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

Aval

B===

C"boolean"

Dval === "boolean"

Attempts:

3 left

💡 Hint

Common Mistakes

Using assignment = instead of comparison ===.

Comparing to boolean without quotes.

Putting the whole expression inside quotes.

The function checks if the type of val is exactly the string "boolean" using typeof val === "boolean".