"Utilize TypeScript to create a function that can handle either a single value or

Question

"Utilize TypeScript to create a function that can handle either a single value or

I am attempting to develop a double function with the following structure:

type MaybeArray<T> = T | T[];

function double<T extends MaybeArray<number>>(data: T): T extends number[] ? number[] : number {
  if (Array.isArray(data)) {
    // TypeScript fails to recognize that `data` is an array of numbers in this section.
    return data.map((n) => double(n));
  }

  // TypeScript fails to recognize that `data` is a number outside the previous condition.
  return data * 2;
}

^{Playground link.}

The goal is for the function to output the doubled value of the provided number, or an array with the doubled values if given a list. Please refer to any errors in the linked playground above.

However, TypeScript struggles to identify whether the parameter `data` within the if block is an array of numbers and recognizes it as a plain number outside the block.

Is there a way to correct this issue without utilizing any overloads?

P.S.: I acknowledge that employing function overloads could resolve this dilemma, but I am interested in discovering alternative solutions.

typescript

Answer 1

Answer №1

Here is a solution that may help with the issue you mentioned in your post:

You can also consider testing out the following code snippet:

const calculateSum = (arr) => {
    let sum = 0;
    for (let num of arr) {
        sum += num;
    }
    return sum;
};

Answer 2

Here is a solution that may help with the issue you mentioned in your post:

You can also consider testing out the following code snippet:

const calculateSum = (arr) => {
    let sum = 0;
    for (let num of arr) {
        sum += num;
    }
    return sum;
};

"Utilize TypeScript to create a function that can handle either a single value or

Answer №1

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