example to log undefined vals (related to pull #473)

Also, a changelog update for a recent change.

CHANGES.md

@@ -7,6 +7,8 @@ Known issues:
 
 ## not yet released
 
+- [pull #469] Fix a strict mode (`"use strict;"`) error in some versions of
+  Safari.
 
 ## 1.8.8
 

examples/log-undefined-values.js

@@ -0,0 +1,60 @@
+#!/usr/bin/env node
+/* BEGIN JSSTYLED */
+/**
+ * <https://github.com/trentm/node-bunyan/pull/473> is a change to add a
+ * feature to Bunyan's log record stringification to log `undefined` values.
+ * Let's attempt that with a custom raw stream.
+ *
+ * Note that a raw stream here isn't ideal, because using a custom raw stream
+ * means that it is a pain to use some of the other built-in stream types
+ * (file, rotating-file). However, it might be a satisfactory workaround for
+ * some.
+ *
+ * Example:
+ *      $ node log-undefined-values.js
+ *      {"name":"log-undefined-values","hostname":"danger0.local","pid":28161,"level":30,"anull":null,"aundef":"[Undefined]","anum":42,"astr":"foo","msg":"hi","time":"2017-03-04T20:53:54.331Z","v":0}
+ *      $ node log-undefined-values.js | bunyan
+ *      [2017-03-04T20:54:41.874Z]  INFO: log-undefined-values/28194 on danger0.local: hi (anull=null, aundef=[Undefined], anum=42, astr=foo)
+ */
+/* END JSSTYLED */
+
+var bunyan = require('../lib/bunyan');
+var fs = require('fs');
+
+
+function replacer() {
+    // Note: If node > 0.10, then could use Set here (see `safeCyclesSet()`
+    // in bunyan.js) for a performance improvement.
+    var seen = [];
+    return function (key, val) {
+        if (val === undefined) {
+            return '[Undefined]';
+        } else if (!val || typeof (val) !== 'object') {
+            return val;
+        }
+        if (seen.indexOf(val) !== -1) {
+            return '[Circular]';
+        }
+        seen.push(val);
+        return val;
+    };
+}
+
+function LogUndefinedValuesStream(stream) {
+    this.stream = stream;
+}
+LogUndefinedValuesStream.prototype.write = function (rec) {
+    var str = JSON.stringify(rec, replacer()) + '\n';
+    this.stream.write(str);
+}
+
+var log = bunyan.createLogger({
+    name: 'log-undefined-values',
+    streams: [ {
+        level: 'info',
+        type: 'raw',
+        stream: new LogUndefinedValuesStream(process.stdout)
+    } ]
+});
+
+log.info({anull: null, aundef: undefined, anum: 42, astr: 'foo'}, 'hi');