20 lines
817 B
TypeScript
20 lines
817 B
TypeScript
/**
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* Calculates the sum of an array of numbers when applying
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* the `getValue` function to each element.
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*
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* If the array is empty, this function returns `0`.
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*
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* @template T - The type of elements in the array.
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* @param {readonly T[]} items - An array to calculate the sum.
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* @param {(element: T, index: number) => number} getValue - A function that selects a numeric value from each element.
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* It receives the element and its zero‑based index in the array.
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* @returns {number} The sum of all the numbers as determined by the `getValue` function.
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*
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* @example
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* sumBy([{ a: 1 }, { a: 2 }, { a: 3 }], (x, i) => x.a * i); // Returns: 8
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* sumBy([], () => 1); // Returns: 0
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*/
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declare function sumBy<T>(items: readonly T[], getValue: (element: T, index: number) => number): number;
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export { sumBy };
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