isNumeric

1/**
2 * Checks if a value is a finite number or a numeric string.
3 *
4 * @param value - The value to check.
5 * @returns True if the value is numeric, false otherwise.
6 */
7export function isNumeric(value: any): boolean {
8  return (
9    (typeof value === 'number' && isFinite(value)) ||
10    (typeof value === 'string' && value.trim() !== '' && !isNaN(Number(value)))
11  );
12}

• Supports Both Numbers and Numeric Strings

  Handles common input types like 42 and '42.5', improving flexibility in mixed-type environments.

• Robust Whitespace Handling

  Trims string inputs before evaluation to avoid false negatives due to leading/trailing spaces.

• Safe Against NaN and Infinities

  Explicitly filters out NaN, Infinity, and -Infinity, ensuring only valid finite numbers pass.

• Practical and Lightweight

  Simple logic covers a broad range of real-world cases without relying on regex or external libraries.

Tests | Examples

1test('isNumeric - with valid numbers', () => {
2  expect(isNumeric(42)).toBe(true);
3  expect(isNumeric(-3.14)).toBe(true);
4  expect(isNumeric('5')).toBe(true);
5  expect(isNumeric('  7.5 ')).toBe(true);
6});
7
8test('isNumeric - with invalid values', () => {
9  expect(isNumeric(NaN)).toBe(false);
10  expect(isNumeric(Infinity)).toBe(false);
11  expect(isNumeric(undefined)).toBe(false);
12  expect(isNumeric(null)).toBe(false);
13  expect(isNumeric('')).toBe(false);
14  expect(isNumeric('abc')).toBe(false);
15  expect(isNumeric([])).toBe(false);
16  expect(isNumeric({})).toBe(false);
17});

Common Use Cases

• User Input Validation

  Check if form inputs or query parameters can be safely parsed as numbers.

• Data Parsing from CSV/JSON

  Identify numeric fields when reading values from loosely typed data sources.

• Sanity Checks in Dynamic Code

  Prevent runtime errors by verifying values before performing numeric operations.

• Filtering and Cleanup

  Remove or flag non-numeric values from datasets, especially when imported from untrusted sources.

• Conditional Type Coercion

  Safely convert values to numbers only when appropriate, avoiding NaN pollution.