flexible array type for typescript

Question

Say I wanted to encode an array, which could have either length 1 or 2 into typescript. Say I furthermore wanted to limit the first element in the array to be one of a specific number of strings, eg:

type fruit = 'banana' | 'apple' | 'passionfruit' | 'kiwi'

while the second key was flexible.

something like:

declare interface ObjectExample {
  fruit: fruit,
  other?: string
}

but for an array. How would I go about doing this?

score 1 · Accepted Answer · 2017-05-23 14:11:16Z

1

This would be:

type ObjectExample = [fruit] | [fruit, any];

However, this will not prevent you from assigning or accessing a third element on the array. From the TS docs:

When accessing an element outside the set of known indices, a union type is used instead:

In that sense, unless you want to constrain the type of the second element, the above is equivalent to

type ObjectExample = [fruit];

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