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typescript

TS2556: A spread argument must either have a tuple type or be passed to a rest parameter

You're spreading an array into a function call, but TypeScript can't verify that the array's contents match the function's parameters. Spreading works safely when the array is a tuple (fixed length and types) or the function accepts rest parameters.

Common causes

Spreading a general array (string[], number[]) into a function that expects specific individual arguments
Dynamically building an argument list as an array and spreading it into a typed function
The spread value is typed as an array and the function has a specific, fixed signature
Using apply() alternatives with spread where the argument types can't be verified

How to fix it

Type the array as a tuple: const args: [string, number] = ['hello', 42]; fn(...args)
Use as const to make the array a tuple: const args = ['hello', 42] as const
Change the function to accept rest parameters: function fn(...args: [string, number])
Pass arguments individually rather than spreading if the list is short

Example

function add(a: number, b: number): number { return a + b; }
const args = [1, 2];
add(...args);
// error TS2556: A spread argument must either have a tuple type or be passed to a rest parameter.

Spreading a number[] array into a function — TypeScript can't verify the element count or types match

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