Tuple type definition in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a tuple type in TypeScript?

A tuple type in TypeScript is an array with a fixed number of elements where each element can have a different type. It defines the exact types and order of elements.

beginner

How do you define a tuple type with a string and a number in TypeScript?

You define it like this: <code>let example: [string, number];</code> This means the first element must be a string and the second a number.

intermediate

Can tuple elements be optional in TypeScript? How?

Yes, tuple elements can be optional by adding a question mark after the type. Example: <code>let example: [string, number?];</code> means the second element can be a number or undefined.

beginner

What happens if you try to assign wrong types to a tuple in TypeScript?

TypeScript will show an error because tuples expect specific types in a fixed order. For example, assigning a number where a string is expected will cause a type error.

advanced

How can you use rest elements in tuple types?

You can use rest elements to allow a variable number of elements of the same type at the end. Example: <code>let example: [string, ...number[]];</code> means one string followed by any number of numbers.

How do you declare a tuple with a boolean and a string in TypeScript?

A let t: [boolean, string];

B let t: (boolean | string)[];

C let t: boolean, string;

D let t: {boolean, string};

Option A correctly declares a tuple with a boolean followed by a string. Option B is an array of boolean or string, not a tuple.

What is true about tuple types in TypeScript?

A They have fixed length and fixed types per position.

B They can only contain elements of the same type.

C They are the same as arrays.

D They cannot have optional elements.

Tuples have fixed length and each position has a specific type. Arrays can have variable length and usually one type.

How do you make the last element of a tuple a variable number of strings?

A let t: [number, string?];

B let t: [number, string];

C let t: [number, ...string[]];

D let t: [number, string[]];

Option C uses rest syntax to allow any number of strings after a number.

What error occurs if you assign [42, 'hello'] to let t: [string, number]?

A Syntax error.

B No error, assignment is valid.

C Runtime error only.

D Type error because the first element should be string, not number.

The tuple expects a string first, but 42 is a number, so TypeScript shows a type error.

Can tuple types have optional elements in TypeScript?

A Only the first element can be optional.

B Yes, by adding a question mark after the type.

C No, tuples must always have all elements.

D Optional elements are only for arrays.

You can mark tuple elements optional with a question mark, e.g., [string, number?].

Explain what a tuple type is in TypeScript and how it differs from a regular array.

Think about how many elements and what types each element can have.

Describe how to define a tuple with optional and rest elements in TypeScript.

Consider how to allow some elements to be missing or repeated.