percentChange

1/**
2 * Calculates the percentage change from an old value to a new value.
3 *
4 * @param oldValue - The original value.
5 * @param newValue - The new value.
6 * @returns Percentage change, positive or negative.
7 */
8export function percentChange(oldValue: number, newValue: number): number {
9  if (oldValue === 0) {
10    return newValue === 0 ? 0 : Infinity * Math.sign(newValue);
11  }
12  return ((newValue - oldValue) / Math.abs(oldValue)) * 100;
13}

1test('percentChange - increase', () => {
2  expect(percentChange(100, 150)).toBe(50);
3});
4
5test('percentChange - decrease', () => {
6  expect(percentChange(200, 150)).toBe(-25);
7});
8
9test('percentChange - no change', () => {
10  expect(percentChange(42, 42)).toBe(0);
11});
12
13test('percentChange - from zero to positive', () => {
14  expect(percentChange(0, 10)).toBe(Infinity);
15});
16
17test('percentChange - from zero to negative', () => {
18  expect(percentChange(0, -10)).toBe(-Infinity);
19});
20
21test('percentChange - both zero', () => {
22  expect(percentChange(0, 0)).toBe(0);
23});