Template literal type syntax in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a template literal type that combines 'Hello' with a name.

Typescript

type Greeting = `Hello, [1]`;

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

Anumber

Bstring

Cboolean

Dany

Attempts:

3 left

💡 Hint

Common Mistakes

Using number or boolean instead of string inside the template literal.

The template literal type expects a string to combine with 'Hello,'.

2fill in blank

medium

Complete the code to create a type that prefixes 'ID_' to a number converted to string.

Typescript

type ID = `ID_[1]`;

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

Aboolean

Bnumber

Cstring

Dsymbol

Attempts:

3 left

💡 Hint

Common Mistakes

Using number directly inside the template literal type without converting to string.

The template literal type requires a string type inside the backticks to concatenate.

3fill in blank

hard

Fix the error in the template literal type that tries to combine a boolean with a string.

Typescript

type Flag = `is[1]`;

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

Aboolean

Bany

Cnumber

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using boolean or number types inside template literal types.

Template literal types can only combine string types, so 'string' is correct.

4fill in blank

hard

Fill both blanks to create a template literal type that combines a prefix and a suffix string.

Typescript

type FullName = `$[1]$[2]`;

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

AFirstName

Bnumber

CLastName

Dboolean

Attempts:

3 left

💡 Hint

Common Mistakes

Using number or boolean types instead of string types for name parts.

The template literal type combines two string types: FirstName and LastName.

5fill in blank

hard

Fill all three blanks to create a template literal type that formats a date string as 'YYYY-MM-DD'.

Typescript

type DateString = `$[1]-[2]-[3]`;

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

AYear

BMonth

CDay

DHour

Attempts:

3 left

💡 Hint

Common Mistakes

Including non-date parts like Hour or using wrong order in the template literal.

The template literal type combines Year, Month, and Day string types to form a date.

Practice

1. What does a template literal type in TypeScript do?

easy

A. Defines a function that returns a string.

B. Creates new string types by combining other string types using backticks and ${}.

C. Declares a variable with a fixed string value.

D. Creates a number type from string literals.

Solution

1. Step 1: Understand template literal types

   Template literal types use backticks and ${} to combine string types into new string types.

2. Step 2: Compare options

   Only Creates new string types by combining other string types using backticks and ${}. correctly describes this behavior; others describe unrelated concepts.

3. Final Answer:

   Creates new string types by combining other string types using backticks and ${}. -> Option B

4. Quick Check:

   Template literal types combine strings = A [OK]

Hint: Remember: template literal types build new string types with `${}` [OK]

Common Mistakes:

• Confusing template literal types with string variables
• Thinking template literals create functions
• Assuming they create number types

2. Which of the following is the correct syntax for a template literal type in TypeScript?

easy

A. type Greeting = ${string} world;

B. type Greeting = '${string} world';

C. type Greeting = "${string} world";

D. type Greeting = `${string} world`;

Solution

1. Step 1: Identify correct template literal syntax

   Template literal types use backticks (`) around the string with ${} for type insertion.

2. Step 2: Check each option

   Only `type Greeting = `${string} world`;` uses backticks correctly; the others use single/double quotes or miss backticks.

3. Final Answer:

   type Greeting = `${string} world`; -> Option D

4. Quick Check:

   Backticks + ${} = A [OK]

Hint: Use backticks ``, not quotes, for template literal types [OK]

Common Mistakes:

• Using single or double quotes instead of backticks
• Omitting backticks entirely
• Placing ${} outside backticks

3. Given the code:

type Name = "Alice" | "Bob";
type Greeting = `Hello, ${Name}!`;

let greet1: Greeting = "Hello, Alice!";
let greet2: Greeting = "Hello, Charlie!";

Which line causes a TypeScript error?

medium

A. let greet2: Greeting = "Hello, Charlie!";

B. let greet1: Greeting = "Hello, Alice!";

C. Both lines cause errors

D. Neither line causes an error

Solution

1. Step 1: Understand the Greeting type

   Greeting is a template literal type combining "Hello, " with Name ("Alice" or "Bob") and "!".

2. Step 2: Check assigned values

   "Hello, Alice!" matches Greeting, but "Hello, Charlie!" does not because "Charlie" is not in Name.

3. Final Answer:

   let greet2: Greeting = "Hello, Charlie!"; -> Option A

4. Quick Check:

   Invalid string not in union = B [OK]

Hint: Check if inserted string matches union type exactly [OK]

Common Mistakes:

• Assuming any string fits template literal type
• Ignoring union type restrictions
• Confusing variable assignment with type definition

4. Identify the error in this TypeScript code using template literal types:

type Status = "success" | "error";
type Message = `${Status}` | number;

let msg: Message = 404;

medium

A. There is no error; the code is valid.

B. The template literal type syntax is incorrect; it needs backticks.

C. The variable msg cannot be assigned a number if Message includes number.

D. Template literal types cannot be combined with number types using |.

Solution

1. Step 1: Analyze the type Message

   Message is a union of a template literal type `${Status}` (which is "success" or "error") and number.

2. Step 2: Check variable assignment

   Assigning 404 (a number) to msg is valid because Message includes number.

3. Final Answer:

   There is no error; the code is valid. -> Option A

4. Quick Check:

   Union allows number assignment = D [OK]

Hint: Union types allow multiple types including template literals and numbers [OK]

Common Mistakes:

• Thinking template literals can't be unioned with other types
• Assuming syntax error in template literal usage
• Believing number assignment is invalid here

5. How can you create a type that represents all possible CSS margin properties like "margin-top", "margin-right", "margin-bottom", and "margin-left" using template literal types?

hard

A. type MarginProperty = `margin-${string}`;

B. type MarginProperty = "margin-top" | "margin-right" | "margin-bottom" | "margin-left";

C. type MarginProperty = `margin-${"top" | "right" | "bottom" | "left"}`;

D. type MarginProperty = `margin-${number}`;

Solution

1. Step 1: Understand the goal

   Create a type for specific margin sides using template literal types with a union of side strings.

2. Step 2: Evaluate options

   type MarginProperty = `margin-${"top" | "right" | "bottom" | "left"}`; uses template literal with union of exact sides, producing only valid margin properties. type MarginProperty = "margin-top" | "margin-right" | "margin-bottom" | "margin-left"; works but is not using template literals. type MarginProperty = `margin-${string}`; allows any string after "margin-", which is too broad. type MarginProperty = `margin-${number}`; uses number, which is invalid here.

3. Final Answer:

   type MarginProperty = `margin-${"top" | "right" | "bottom" | "left"}`; -> Option C

4. Quick Check:

   Template literal + union for sides = C [OK]

Hint: Use union inside ${} to limit template literal options [OK]

Common Mistakes:

• Using string instead of union inside template literal
• Listing all options without template literals
• Using number instead of string union