Find the index of the minimum item of an array

JavaScript version
const indexOfMin = (arr) => arr.reduce((prev, curr, i, a) => (curr < a[prev] ? i : prev), 0);
TypeScript version
const indexOfMin = (arr: number[]): number => arr.reduce((prev, curr, i, a) => (curr < a[prev] ? i : prev), 0);
Examples
indexOfMin([6, 4, 8, 2, 10]); // 3
indexOfMin([6, 4, 2, 2, 10]); // 2