TypeScript array with minimum length

Question

How can you create a type in TypeScript that only accepts arrays with two or more elements?

needsTwoOrMore([\"onlyOne\"]) // should have error
needsTwoOrMore         


        

Answer 1

This is an old question and the answer is fine (it helped me as well), but I just stumbled across this solution as well while playing.

I had already defined a typed Tuple (type Tuple = [T, T];), and then below that, I had defined array of two or more as described above (type ArrayOfTwoOrMore = { 0: T, 1: T } & T[];).

It occurred to me to try using the Tuple structure in place of { 0: T, 1: T }, like so:

type ArrayOfTwoOrMore = [T, T, ...T[]];

And it worked. Nice! It's a little more concise and perhaps able to be clearer in some use-cases.

Worth noting is that a tuple doesn't have to be two items of the same type. Something like ['hello', 2] is a valid tuple. In my little code snippet, it just happens to be a suitable name and it needs to contain two elements of the same type.