Add utility belt example

examples/utility-belt/src/string-to-number.js

@@ -0,0 +1,14 @@
+/**
+ * Converts a string to a number or throws an error if the string is not a number.
+ * @param {string} value
+ * @returns {number} The number.
+ */
+export const stringToNumber = (value) => {
+  const number = Number(value);
+
+  if (isNaN(number)) {
+    throw new Error(`'${value}' cannot be parsed as a number.`);
+  }
+
+  return number;
+};

examples/utility-belt/src/string-to-number.test.js

@@ -0,0 +1,15 @@
+import { describe, it, expect } from 'vitest';
+import { stringToNumber } from './string-to-number';
+
+describe('stringToNumber', () => {
+  it('converts a string to a number', () => {
+    expect(stringToNumber('42')).toBe(42);
+  });
+
+  it('throws an error if given a string that is not a number', () => {
+    const value = 'foo';
+    expect(() => stringToNumber(value)).toThrowError(
+      `cannot be parsed as a number`,
+    );
+  });
+});