percentDiff

1/**
2 * Calculates the percentage difference between two numbers.
3 *
4 * @param a - The original number.
5 * @param b - The new number.
6 * @returns The percent difference from 'a' to 'b'.
7 */
8export function percentDiff(a: number, b: number): number {
9  if (a === 0) {
10    return b === 0 ? 0 : Infinity;
11  }
12  return ((b - a) / Math.abs(a)) * 100;
13}

• Handles Zero Safely

  Includes logic to avoid division-by-zero errors and distinguish between zero-to-zero and zero-to-nonzero cases.

• Directional Insight

  Preserves the sign of the difference, indicating whether the value increased or decreased.

• Mathematically Accurate

  Uses absolute value of the base (a) to correctly calculate percentage change relative to magnitude.

• Concise and Readable

  Simple logic with clear structure, making it easy to understand and maintain.

Tests | Examples

1test('percentDiff - positive increase', () => {
2  expect(percentDiff(100, 150)).toBe(50);
3});
4
5test('percentDiff - positive decrease', () => {
6  expect(percentDiff(200, 150)).toBeCloseTo(-25);
7});
8
9test('percentDiff - no change', () => {
10  expect(percentDiff(42, 42)).toBe(0);
11});
12
13test('percentDiff - zero to non-zero (infinity)', () => {
14  expect(percentDiff(0, 100)).toBe(Infinity);
15});
16
17test('percentDiff - zero to zero', () => {
18  expect(percentDiff(0, 0)).toBe(0);
19});
20
21test('percentDiff - handles negative base', () => {
22  expect(percentDiff(-100, -50)).toBe(50);
23  expect(percentDiff(-100, -200)).toBe(-100);
24});

Common Use Cases

• Analytics and Dashboards

  Show percentage change in metrics like revenue, traffic, or conversion rate over time.

• Finance and Investment

  Calculate percent gain or loss in stock prices, portfolio value, or earnings reports.

• Reporting and Comparison

  Highlight performance changes between current and previous periods in reports.

• User Feedback or Notifications

  Notify users when a tracked value changes significantly in either direction.

• Testing and Benchmarking

  Evaluate percent improvement or regression in performance metrics between versions or builds.