Use typescript to extract all element type(s) from array except first

Question

Say I have the type

type MyTypeArray = ['', 2, boolean]

How could I extract the type 2 | boolean when the array could be of an unknown length?

captain-yossarian from Ukraine · Accepted Answer · 2021-09-19 16:22:17Z

5

You can infer all elements but first. Use spread tuple operator: ..., just like in plain javascript


type ExtractTail<T extends any[]> = T extends [infer _, ...infer Tail] ? Tail : never

// [2, boolean]
type MyTypeArray = ExtractTail<['', 2, boolean]>

// 2 | boolean
type Union = MyTypeArray[number]

edited Sep 19, 2021 at 16:22

answered Sep 19, 2021 at 15:56

captain-yossarian from Ukraine

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2 Comments

captain-yossarian from Ukraine Over a year ago

@johann1301s made an update.

Austin Over a year ago

You can also use a similar procedure to extract just the last element of a tuple: type LastValueOfTuple<T extends any[] | readonly any[]> = T extends [...infer Start, infer Last] ? Last : never; Not the question that was asked, but this is the article that appeared when I was searching for this answer.

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