Rest elements in tuples in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a rest element in a tuple in TypeScript?

A rest element in a tuple allows you to capture multiple elements into a single array within the tuple. It uses the syntax ...name to gather remaining elements.

beginner

How do you declare a tuple with a rest element that captures numbers in TypeScript?

You can declare it like this: type Numbers = [string, ...number[]]; This means the first element is a string, followed by zero or more numbers.

intermediate

Can rest elements in tuples be placed anywhere other than the end?

No, rest elements must be the last element in a tuple type. This is because they capture all remaining elements.

beginner

What is the type of a rest element in a tuple?

The rest element type is always an array type. For example, ...number[] means the rest elements are numbers collected into an array.

beginner

Example: What is the type of <code>const t: [string, ...boolean[]]</code>?

It means t is a tuple where the first element is a string, followed by zero or more boolean values.

In TypeScript, where must the rest element appear in a tuple type?

A At the beginning

B In the middle

C At the end

D Anywhere

Rest elements must always be the last element in a tuple type to capture all remaining elements.

What does the tuple type [number, ...string[]] represent?

A A tuple with only numbers

B A tuple with any types

C A tuple with only strings

D A tuple starting with a number, followed by zero or more strings

The first element is a number, and the rest are strings collected into an array.

What type is the rest element ...boolean[] in a tuple?

A A single boolean

B An array of booleans

C A tuple of booleans

D A number

The rest element collects multiple booleans into an array.

Can you have multiple rest elements in a single tuple type?

A No, only one rest element at the end

B Yes, anywhere

C Yes, but only at the start

D Yes, but only in the middle

Only one rest element is allowed and it must be at the end of the tuple.

Which of these is a valid tuple type with a rest element?

A [number, ...string[]]

B [string, number, ...boolean, string]

C [...string[], number]

D [...number[], ...string[]]

Only option C has the rest element at the end and is valid syntax.

Explain what a rest element in a tuple is and how it is used in TypeScript.

Think about how you gather leftover items in a list.

Write a tuple type with a string first element and any number of boolean elements after it.

Use ...boolean[] after the string.