Set the default child logger level to inherit from the root logger

This sets the default child logger level to inherit from the root
logger. To maintain backwards compatibility, the default root logger
is now instantiated with `{ level: 'debug' }` when one was not
provided through `setRootLogger`.

README.md

@@ -68,10 +68,12 @@ const logger = debino('root')('foo', { level: 'info' });
 ```
 
 You may also set the log level via the `LOG_LEVEL` environment variable. However, the `level` option will always take precedence over it.
+If both `level` and `LOG_LEVEL` are not set, it will use the value from
+the root logger (See the [Root Logger](#root-logger) section below for more information).
 
 ### Root logger
 
-Every call to `debino` creates a child logger based on a root logger. The default root logger is an instance returned by `pino()`, without any options. You may set your own root logger by calling `setRootLogger()`:
+Every call to `debino` creates a child logger based on a root logger. The default root logger is an instance returned by `pino({ level: 'debug' })`. You may set your own root logger by calling `setRootLogger()`:
 
 ```js
 import { debino, pino, setRootLogger } from '@uphold/debino';

src/index.js

@@ -55,7 +55,7 @@ const debino = (namespace, { prefix = 'sub', suffix = 'component', ...options }
 
   // Ensure the root logger is set.
   if (!rootLogger) {
-    rootLogger = global[globalSymbol].rootLogger = pino();
+    rootLogger = global[globalSymbol].rootLogger = pino({ level: 'debug' });
   }
 
   // Create the logger for this namespace if it doesn't exist.
@@ -68,7 +68,7 @@ const debino = (namespace, { prefix = 'sub', suffix = 'component', ...options }
 
   // Set the log level based on the debug namespace.
   if (debug.enabled(namespace)) {
-    childLogger.level = options.level ?? process.env.LOG_LEVEL ?? 'debug';
+    childLogger.level = options.level ?? process.env.LOG_LEVEL ?? rootLogger.level;
   } else {
     childLogger.level = 'silent';
   }

src/index.test.js

@@ -74,6 +74,15 @@ describe('debino', () => {
     expect(logger.level).toEqual('warn');
   });
 
+  it('should be on the specified level on the root logger if `DEBUG` matches logger name', () => {
+    debug.enable('abc');
+    setRootLogger(pino({ level: 'warn' }));
+
+    const logger = debino('abc');
+
+    expect(logger.level).toEqual('warn');
+  });
+
   it('should support multiple components separated by colons', () => {
     const logger = debino('foo:bar:biz:qux');
     const bindings = logger.bindings();