typeof type guards in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the variable is a string using typeof.

Typescript

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

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

A"string"

B"number"

C"boolean"

D"object"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'string' without quotes.

Comparing to 'String' with uppercase S.

Using typeof value === string (missing quotes).

The typeof operator returns "string" for string values, so we compare with "string".

2fill in blank

medium

Complete the code to check if the variable is a number using typeof.

Typescript

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

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

A"undefined"

B"string"

C"boolean"

D"number"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Number' with uppercase N.

Comparing to 'num' instead of 'number'.

Missing quotes around 'number'.

typeof returns "number" for numeric values, so we compare with "number".

3fill in blank

hard

Fix the error in the typeof check to correctly identify a boolean.

Typescript

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

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

A"string"

B"bool"

C"boolean"

D"Boolean"

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase "Boolean" instead of lowercase.

Using "bool" which is not a valid typeof result.

Missing quotes around the type string.

The typeof operator returns "boolean" for boolean values, all lowercase.

4fill in blank

hard

Fill both blanks to create a type guard that checks if input is a string or a number.

Typescript

if (typeof input === [1] || typeof input === [2]) {
  console.log("Input is string or number");
}

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

A"string"

B"boolean"

C"number"

D"object"

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect type strings like "bool" or "object".

Using && instead of || which requires both types at once.

Missing quotes around type strings.

We check if input is either "string" or "number" using typeof comparisons.

5fill in blank

hard

Fill all three blanks to create a function that returns the type of the value as a string using typeof.

Typescript

function getType(value: unknown): string {
  return typeof [1] [2] [3];
}

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

Avalue

B+

C""

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' instead of '+' for concatenation.

Not using quotes around the empty string.

Using a variable name other than 'value'.

The function returns typeof value concatenated with an empty string to ensure the return type is string.