From d4ec38097f833229f021deadc35d75c433a5231b Mon Sep 17 00:00:00 2001
From: Linus Groh <mail@linusgroh.de>
Date: Wed, 29 Apr 2020 00:22:47 +0100
Subject: [PATCH] LibJS: Return undefined in Array.prototype.{pop,shift} for
 empty values

---
 Libraries/LibJS/Runtime/ArrayPrototype.cpp     | 4 ++--
 Libraries/LibJS/Tests/Array.prototype.pop.js   | 2 ++
 Libraries/LibJS/Tests/Array.prototype.shift.js | 2 ++
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/Libraries/LibJS/Runtime/ArrayPrototype.cpp b/Libraries/LibJS/Runtime/ArrayPrototype.cpp
index eb40a51f47..29505a270c 100644
--- a/Libraries/LibJS/Runtime/ArrayPrototype.cpp
+++ b/Libraries/LibJS/Runtime/ArrayPrototype.cpp
@@ -207,7 +207,7 @@ Value ArrayPrototype::pop(Interpreter& interpreter)
         return {};
     if (array->elements().is_empty())
         return js_undefined();
-    return array->elements().take_last();
+    return array->elements().take_last().value_or(js_undefined());
 }
 
 Value ArrayPrototype::shift(Interpreter& interpreter)
@@ -217,7 +217,7 @@ Value ArrayPrototype::shift(Interpreter& interpreter)
         return {};
     if (array->elements().is_empty())
         return js_undefined();
-    return array->elements().take_first();
+    return array->elements().take_first().value_or(js_undefined());
 }
 
 static Value join_array_with_separator(Interpreter& interpreter, const Array& array, StringView separator)
diff --git a/Libraries/LibJS/Tests/Array.prototype.pop.js b/Libraries/LibJS/Tests/Array.prototype.pop.js
index 9dce8d4c29..a4d09a2311 100644
--- a/Libraries/LibJS/Tests/Array.prototype.pop.js
+++ b/Libraries/LibJS/Tests/Array.prototype.pop.js
@@ -13,6 +13,8 @@ try {
     assert(value === undefined);
     assert(a.length === 0);
 
+    assert([,].pop() === undefined);
+
     console.log("PASS");
 } catch (e) {
     console.log("FAIL: " + e);
diff --git a/Libraries/LibJS/Tests/Array.prototype.shift.js b/Libraries/LibJS/Tests/Array.prototype.shift.js
index 44cb316203..2b48e7bf20 100644
--- a/Libraries/LibJS/Tests/Array.prototype.shift.js
+++ b/Libraries/LibJS/Tests/Array.prototype.shift.js
@@ -13,6 +13,8 @@ try {
     assert(value === undefined);
     assert(a.length === 0);
 
+    assert([,].shift() === undefined);
+
     console.log("PASS");
 } catch (e) {
     console.log("FAIL: " + e);