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Derek Nguyen
Derek Nguyen

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A spread argument must either have a tuple type or be passed to a rest parameter. ts(2556)

You want to pass variable args to a function, like so:

const doSomething = (a: string, b?: string, c?: string): void => {};
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However, TS didn't like it...

// não bom const args = [['a', 'b', 'c'], ['a', 'b'], ['a']]; args.forEach((arg) => { // A spread argument must either // have a tuple type or be passed  // to a rest parameter. ts(2556) vvvvvv doSomething(...arg); })
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The problem is that doSomething expects one to three arguments of type string, but arg is typed as string[]. We need to narrow the type down, to match the arguments of doSomething()

// bom const properTypedArgs: [a: string, b?: string, c?: string][] = [['a', 'b', 'c'], ['a', 'b'], ['a']]; properTypedArgs.forEach((arg) => { doSomething(...arg); })
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This works, but if you don't fancy re-typing the function's argument type defs or don't have it handy, TS utility type got you covered:

// ainda melhor const properTypedArgs: Parameters<typeof doSomething>[] = [['a', 'b', 'c'], ['a', 'b'], ['a']]; properTypedArgs.forEach((arg) => { doSomething(...arg); })
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That's all!

TS playground
Parameter<>
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