This is how the JavaScript spread operator allows passing an array as function arguments:
function f(a, b) { console.log(a, b) }
let arr = [1, 2]
f(...arr) // all fine!
TypeScript 5.3.2 does not accept this, however:
function f(a, b) { console.log(a, b) }
let arr = [1, 2]
f(...arr) // error: A spread argument must either have a tuple type or be passed to a rest parameter.(2556)
To me this is a bug, because valid JavaScript should always be valid TypeScript.
How can I circumvent this error, why does it occur?
Found a long discussion in the TypeScript repo: microsoft/TypeScript#49700.
The problem here is that the default inferred type for arr is number[], so a normal array with unspecified length.
If you explicitly specify arr to be a tuple (compatible with the function signature), e.g. [number, number], it works correctly. E.g.:
function f(a: unknown, b: unknown) { console.log(a, b) }
let arr: [unknown, unknown] = [1, 2]
f(...arr)