sol.js

const testArray = [5, -2, 3, 7, 3, 9, 3, 9, 9, 4, 4, 14, 13, 14, 20, 21, 11, 12];
// const testArray = [5, -2, 3, 6, 7, 8, 6];
// const testArray = [-5, 1, 1];
// const testArray = [1, 2, 3];

const solution = (a) => {
	let cursorX = 0;
	let cursorY = 0;
	let cursorZ = 0;
	let hasLowerValue = true;

	while (cursorX < a.length) {
		const valueX = a[cursorX];
		const valueY = a[cursorY];
		const valueZ = a[cursorZ];

		if (valueX < valueZ) {
			hasLowerValue = true;
		}

		if (valueX > valueY && hasLowerValue) {
			cursorZ = cursorY;
			cursorY = cursorX;

			hasLowerValue = false;
		}

		cursorX++;
	}

	return cursorY;
};

console.log(solution(testArray));