From df6696f5762a8cdd31ab225f8e71ddd12b593722 Mon Sep 17 00:00:00 2001
From: Kesse Jones <kjonesfc@outlook.com>
Date: Mon, 20 Apr 2020 10:39:39 -0300
Subject: LibJS: Add Array.prototype.reverse

---
 Libraries/LibJS/Runtime/ArrayPrototype.cpp       | 22 +++++++++++++++++
 Libraries/LibJS/Runtime/ArrayPrototype.h         |  1 +
 Libraries/LibJS/Tests/Array.prototype.reverse.js | 31 ++++++++++++++++++++++++
 3 files changed, 54 insertions(+)
 create mode 100644 Libraries/LibJS/Tests/Array.prototype.reverse.js

diff --git a/Libraries/LibJS/Runtime/ArrayPrototype.cpp b/Libraries/LibJS/Runtime/ArrayPrototype.cpp
index d3e881d81d..c063085419 100644
--- a/Libraries/LibJS/Runtime/ArrayPrototype.cpp
+++ b/Libraries/LibJS/Runtime/ArrayPrototype.cpp
@@ -54,6 +54,7 @@ ArrayPrototype::ArrayPrototype()
     put_native_function("concat", concat, 1);
     put_native_function("slice", slice, 2);
     put_native_function("indexOf", index_of, 1);
+    put_native_function("reverse", reverse, 0);
     put("length", Value(0));
 }
 
@@ -343,4 +344,25 @@ Value ArrayPrototype::index_of(Interpreter& interpreter)
 
     return Value(-1);
 }
+
+Value ArrayPrototype::reverse(Interpreter& interpreter)
+{
+    auto* array = array_from(interpreter);
+    if (!array)
+        return {};
+
+    if (array->elements().size() == 0)
+        return array;
+
+    Vector<Value> array_reverse;
+    array_reverse.ensure_capacity(array->elements().size());
+
+    for (ssize_t i = array->elements().size() - 1; i >= 0; --i)
+        array_reverse.append(array->elements().at(i));
+
+    array->elements() = move(array_reverse);
+
+    return array;
+}
+
 }
diff --git a/Libraries/LibJS/Runtime/ArrayPrototype.h b/Libraries/LibJS/Runtime/ArrayPrototype.h
index 50afdced8b..168827dcb5 100644
--- a/Libraries/LibJS/Runtime/ArrayPrototype.h
+++ b/Libraries/LibJS/Runtime/ArrayPrototype.h
@@ -51,5 +51,6 @@ private:
     static Value concat(Interpreter&);
     static Value slice(Interpreter&);
     static Value index_of(Interpreter&);
+    static Value reverse(Interpreter&);
 };
 }
diff --git a/Libraries/LibJS/Tests/Array.prototype.reverse.js b/Libraries/LibJS/Tests/Array.prototype.reverse.js
new file mode 100644
index 0000000000..2b782fa154
--- /dev/null
+++ b/Libraries/LibJS/Tests/Array.prototype.reverse.js
@@ -0,0 +1,31 @@
+load("test-common.js");
+
+try {
+    assert(Array.prototype.reverse.length === 0);
+
+    var array = [1, 2, 3];
+    
+    assert(array[0] === 1);
+    assert(array[1] === 2);
+    assert(array[2] === 3);
+    
+    array.reverse();
+    
+    assert(array[0] === 3);
+    assert(array[1] === 2);
+    assert(array[2] === 1);
+    
+    var array_ref = array.reverse();
+    
+    assert(array_ref[0] === 1);
+    assert(array_ref[1] === 2);
+    assert(array_ref[2] === 3);
+
+    assert(array[0] === 1);
+    assert(array[1] === 2);
+    assert(array[2] === 3);
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}
-- 
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