Number type behavior in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a number variable with value 10.

Typescript

let num: number = [1];

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

A10

Btrue

C'10'

D"10"

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around the number, which makes it a string.

Assigning a boolean value instead of a number.

The number type variable should be assigned a numeric value without quotes.

2fill in blank

medium

Complete the code to check if a number variable is NaN (Not a Number).

Typescript

if (isNaN([1])) {
  console.log("Not a number");
}

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

A"num"

BNaN

Cnum

DNumber

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the variable name as a string.

Passing the NaN constant instead of the variable.

The isNaN function checks if the value passed is NaN. You should pass the variable name without quotes.

3fill in blank

hard

Fix the error in the code to correctly convert a string to a number.

Typescript

let value: number = Number([1]);

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

Aundefined

B"123"

Ctrue

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Passing boolean or null values which convert to 0 or NaN.

Passing undefined which results in NaN.

The Number function converts a string containing digits to a number. The string must be in quotes.

4fill in blank

hard

Fill both blanks to create a number array and get its length.

Typescript

let numbers: number[] = [[1]];
let length: number = numbers[2];

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

A1, 2, 3

Blength

C.length

Dsize

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'length' without the dot.

Using 'size' which is not a property of arrays.

The array is created with numbers separated by commas. To get the length, use the .length property.

5fill in blank

hard

Fill all three blanks to create a map of numbers and filter keys with values greater than 10.

Typescript

const data: Record<string, number> = {a: 5, b: 15, c: 20};
const filtered = Object.fromEntries(
  Object.entries(data).filter(([[1], [2]]) => [3] > 10)
);

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

Akey

Bvalue

Cval

Dk

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent variable names in destructuring.

Comparing the key instead of the value.

In the filter, the destructured array elements are the key and value. The value is compared to 10.