feat: add ability to translate the entire message (fixes #11)

README.md

@@ -210,13 +210,68 @@ Refer to the [Usage documentation](#usage) for common usage examples.
 
 ### `child`
 
+The `child` function has two signatures:
+
+1. Accepts an object.
+2. Accepts a function.
+
+#### Object input
+
 Creates a child logger appending the provided `context` object to the previous logger context.
 
 ```js
 type ChildType = (context: MessageContextType) => LoggerType;
 
 ```
 
+Example:
+
+```js
+import log from 'roarr';
+
+const childLog = log.child({
+  foo: 'bar'
+});
+
+log.debug('foo 1');
+childLog.debug('foo 2');
+
+// {"context":{"logLevel":20},"message":"foo 1","sequence":0,"time":1531914529921,"version":"1.0.0"}
+// {"context":{"foo":"bar","logLevel":20},"message":"foo 2","sequence":1,"time":1531914529922,"version":"1.0.0"}
+
+```
+
+#### Function input
+
+Creates a child logger where every message is intercepted.
+
+```js
+type ChildType = (context: TranslatorType) => LoggerType;
+
+```
+
+Example:
+
+```js
+import log from 'roarr';
+
+const childLog = log.child((message) => {
+  return {
+    ...message,
+    message: message.message.replace('foo', 'bar')
+  }
+});
+
+log.debug('foo 1');
+childLog.debug('foo 2');
+
+// {"context":{"logLevel":20},"message":"foo 1","sequence":0,"time":1531914656076,"version":"1.0.0"}
+// {"context":{"logLevel":20},"message":"bar 2","sequence":1,"time":1531914656077,"version":"1.0.0"}
+
+```
+
+Example:
+
 ### `trace`
 ### `debug`
 ### `info`

src/factories/createLogger.js

@@ -6,7 +6,8 @@ import {
 import type {
   LoggerType,
   MessageContextType,
-  MessageType
+  MessageType,
+  TranslatorType
 } from '../types';
 
 type OnMessageEventHandlerType = (message: MessageType) => void;
@@ -58,7 +59,16 @@ const createLogger = (onMessage: OnMessageEventHandlerType, parentContext: Messa
     });
   };
 
-  log.child = (context: MessageContextType) => {
+  log.child = (context: TranslatorType | MessageContextType) => {
+    if (typeof context === 'function') {
+      return createLogger((message) => {
+        if (typeof context !== 'function') {
+          throw new Error('Unexpected state.');
+        }
+        onMessage(context(message))
+      }, parentContext);
+    }
+
     return createLogger(onMessage, {
       ...parentContext,
       ...context

src/log.js

@@ -7,6 +7,10 @@ import {
 import {
   ROARR_LOG
 } from './config';
+export type {
+  MessageType,
+  TranslatorType
+} from './types';
 
 global.ROARR = createRoarrInititialGlobalState(global.ROARR || {});
 

src/types.js

@@ -26,6 +26,8 @@ export type MessageType = {|
   +version: string
 |};
 
+export type TranslatorType = (message: MessageType) => MessageType;
+
 declare function Logger (
   context: MessageContextType,
   message: string,

test/roarr/roarr.js

@@ -195,6 +195,29 @@ test('appends context to the previous child context (overrides)', (t) => {
   ]);
 });
 
+test('translates child message', (t) => {
+  const log = createLoggerWithHistory();
+
+  log
+    .child((message) => {
+      return {
+        ...message,
+        message: message.message + 'bar'
+      }
+    })
+    ('foo');
+
+  t.deepEqual(log.messages, [
+    {
+      context: {},
+      message: 'foobar',
+      sequence,
+      time,
+      version
+    }
+  ]);
+});
+
 test('convenience methods trace, debug, info, warn, error and fatal prepend a logLevel property', (t) => {
   const log = createLoggerWithHistory();