TypeScript · Senior · Question 10 of 75

What are variadic tuple types?

type Concat<A extends unknown[], B extends unknown[]> = [...A, ...B];

✓Correct answer: Tuples where spreading generic tuples preserves exact element types
2Tuples without a length limit, equivalent to any[] in TS
3Tuples whose elements the compiler lets you reorder

Explanation

Concat<[1, 2], ['a']> → [1, 2, 'a']. This lets you precisely type concat, curry, Promise.all and wrapper functions with prefix arguments.

Further reading

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