feat: added trace keyword to formatter

This adds a stack trace formatted the same way as an error message. This will allow us to debug where logging messages are coming from.

Related #4

Author: tegefaulkes

src/formatting.ts

@@ -7,6 +7,7 @@ const key = Symbol('key');
 const keys = Symbol('keys');
 const date = Symbol('date');
 const msg = Symbol('msg');
+const trace = Symbol('trace');
 
 function format(
   strings: TemplateStringsArray,
@@ -32,6 +33,10 @@ function format(
         result += record.msg;
       } else if (value === level) {
         result += levelToString(record.level);
+      } else if (value === trace) {
+        const errorStack = new Error().stack ?? '';
+        const formattedStack = errorStack.split('\n').splice(7).join('\n');
+        result += '\n' + formattedStack;
       } else {
         result += value.toString();
       }
@@ -43,4 +48,4 @@ function format(
 
 const formatter = format`${level}:${key}:${msg}`;
 
-export { level, key, keys, date, msg, format, formatter };
+export { level, key, keys, date, msg, trace, format, formatter };

tests/index.test.ts

@@ -98,4 +98,20 @@ describe('index', () => {
     childLogger.debug('DEBUG MESSAGE');
     expect(consoleSpy).toHaveBeenCalledWith('DEBUG:root.child:DEBUG MESSAGE');
   });
+  test('Testing logger trace', () => {
+    jest
+      .useFakeTimers('modern')
+      .setSystemTime(new Date('2020-01-01').getTime());
+    const consoleSpy = jest.spyOn(console, 'log');
+    const logger = new Logger('root', LogLevel.NOTSET, [
+      new ConsoleHandler(
+        formatting.format`${formatting.date}:${formatting.msg}${formatting.trace}`,
+      ),
+    ]);
+    logger.debug('DEBUG MESSAGE');
+    expect(consoleSpy).toHaveBeenCalledWith(
+      expect.stringContaining('2020-01-01T00:00:00.000Z:DEBUG MESSAGE'),
+    );
+    expect(consoleSpy).toHaveBeenCalledWith(expect.stringContaining('at'));
+  });
 });