utils: add new timestamp function

This will be used to create suggested file names that include a timestamp.

src/utils/index.test.ts

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: MIT
 // Copyright (c) 2020 The Pybricks Authors
 
-import { assert, defined, ensureError, hex, maybe } from '.';
+import { assert, defined, ensureError, hex, maybe, timestamp } from '.';
 
 test('assert', () => {
     const assertTrue = jest.fn(() => assert(true, 'should not throw'));
@@ -44,3 +44,21 @@ test('ensureError', () => {
     stringToError.toHaveProperty('name', 'Error');
     stringToError.toHaveProperty('message', stringToErrorMessage);
 });
+
+describe('timestamp', () => {
+    it('should not contain spaces', () => {
+        expect(timestamp()).not.toContain(' ');
+    });
+
+    it('should not contain colons', () => {
+        expect(timestamp()).not.toContain(':');
+    });
+
+    it('should not contain periods', () => {
+        expect(timestamp()).not.toContain('.');
+    });
+
+    it('should not contain letters', () => {
+        expect(timestamp()).not.toMatch(/[A-Za-z]/);
+    });
+});

src/utils/index.ts

@@ -63,3 +63,14 @@ export function ensureError(err: unknown): Error {
 
     return Error(String(err));
 }
+
+/**
+ * Gets a timestamp with second resolution suitable for use in a filename.
+ */
+export function timestamp(): string {
+    return new Date()
+        .toISOString()
+        .replace('T', '_')
+        .replaceAll(':', '-')
+        .replace(/\..*$/, '');
+}