Tuple with fixed length and types in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a tuple in TypeScript?

A tuple is a fixed-length array where each element has a specific type. It allows you to store multiple values of different types in a single variable.

beginner

How do you declare a tuple with a fixed length of 3 elements: a string, a number, and a boolean?

You declare it like this: <pre>let myTuple: [string, number, boolean];</pre> This means the tuple must have exactly three elements in that order and type.

intermediate

Can you change the length of a tuple after it is declared?

No, tuples have a fixed length defined by their type. You cannot add or remove elements beyond the declared length without causing a type error.

beginner

What happens if you try to assign a wrong type to a tuple element?

TypeScript will show a type error because each position in the tuple expects a specific type. For example, assigning a string to a number position is not allowed.

beginner

Example: How to access the second element of a tuple [string, number, boolean]?

You access it by index like an array:

myTuple[1]

which will give you the number value because indexes start at 0.

What does the tuple type [string, number] mean?

A A function returning string and number

B An array with exactly two elements: first a string, second a number

C An object with string and number properties

D An array with any number of strings and numbers

A tuple [string, number] means exactly two elements: first a string, second a number.

Can you assign ["hello", 42, true] to a variable typed as [string, number, boolean]?

A No, because booleans are not allowed

B No, because the length is wrong

C Yes, but only if you use type assertion

D Yes, because the types and order match

The tuple [string, number, boolean] matches the value ["hello", 42, true] exactly in type and order.

What happens if you try to push an extra element to a tuple?

A TypeScript will give a type error

B The tuple will accept it without error

C The tuple will convert to an array

D The extra element will be ignored

Tuples have fixed length, so pushing an extra element causes a type error.

How do you declare a tuple with two elements: a boolean and a string?

A let t: [boolean, string];

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

C let t: boolean & string;

D let t: {boolean, string};

The correct tuple syntax is [boolean, string] for fixed length and types.

Which index accesses the first element of a tuple?

A 1

B -1

C 0

D It depends on the tuple

Tuple elements are accessed by zero-based index, so the first element is at index 0.

Explain what a tuple with fixed length and types is in TypeScript and why it is useful.

Think about a small box with fixed slots for different items.

How do you declare and use a tuple with three elements: string, number, and boolean? Give an example.

Remember tuples are like arrays but with fixed types and length.