From 26332b56b16002ab5f1b92b2622d80d7b8384039 Mon Sep 17 00:00:00 2001
From: Mariusz Nowak <medyk@medikoo.com>
Date: Wed, 2 Aug 2017 08:54:57 +0200
Subject: [PATCH] feat(general): optionalChaining utility

---
 optional-chaining.js      | 12 ++++++++++++
 test/optional-chaining.js | 17 +++++++++++++++++
 2 files changed, 29 insertions(+)
 create mode 100644 optional-chaining.js
 create mode 100644 test/optional-chaining.js

diff --git a/optional-chaining.js b/optional-chaining.js
new file mode 100644
index 00000000..f1811279
--- /dev/null
+++ b/optional-chaining.js
@@ -0,0 +1,12 @@
+"use strict";
+
+var isValue = require("./object/is-value");
+
+var slice = Array.prototype.slice;
+
+// eslint-disable-next-line no-unused-vars
+module.exports = function (value, propertyName1 /*, …propertyNamen*/) {
+	var propertyNames = slice.call(arguments, 1), index = 0, length = propertyNames.length;
+	while (isValue(value) && index < length) value = value[propertyNames[index++]];
+	return index === length ? value : undefined;
+};
diff --git a/test/optional-chaining.js b/test/optional-chaining.js
new file mode 100644
index 00000000..1f7d4056
--- /dev/null
+++ b/test/optional-chaining.js
@@ -0,0 +1,17 @@
+"use strict";
+
+module.exports = function (t, a) {
+	var obj = { foo: { bar: "elo", par: null } };
+	a(t(), undefined);
+	a(t(null), null);
+	a(t(obj), obj);
+	a(t(obj, "foo"), obj.foo);
+	a(t(obj, "foo", "bar"), "elo");
+	a(t(obj, "foo", "bar", "slice"), String.prototype.slice);
+	a(t(obj, "foo", "par"), null);
+	a(t(obj, "foo", "par", "marko"), undefined);
+	a(t(obj, "marko"), undefined);
+	a(t(""), "");
+	a(t("", "foo"), undefined);
+	a(t("", "slice"), String.prototype.slice);
+};