From a7b21ec0f4a77e6e7cdf2b57f9255a02539b02f4 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Sun, 5 Apr 2020 18:06:27 +0200
Subject: [PATCH] LibJS: Add Array.prototype.toString()

---
 Libraries/LibJS/Runtime/ArrayPrototype.cpp    | 30 +++++++++++++++++++
 Libraries/LibJS/Runtime/ArrayPrototype.h      |  1 +
 .../LibJS/Tests/Array.prototype.toString.js   |  9 ++++++
 3 files changed, 40 insertions(+)
 create mode 100644 Libraries/LibJS/Tests/Array.prototype.toString.js

diff --git a/Libraries/LibJS/Runtime/ArrayPrototype.cpp b/Libraries/LibJS/Runtime/ArrayPrototype.cpp
index 23a807d0a67..8a295e96a32 100644
--- a/Libraries/LibJS/Runtime/ArrayPrototype.cpp
+++ b/Libraries/LibJS/Runtime/ArrayPrototype.cpp
@@ -25,10 +25,12 @@
  */
 
 #include <AK/Function.h>
+#include <AK/StringBuilder.h>
 #include <LibJS/Heap/Heap.h>
 #include <LibJS/Interpreter.h>
 #include <LibJS/Runtime/Array.h>
 #include <LibJS/Runtime/ArrayPrototype.h>
+#include <LibJS/Runtime/Error.h>
 #include <LibJS/Runtime/Value.h>
 
 namespace JS {
@@ -38,6 +40,7 @@ ArrayPrototype::ArrayPrototype()
     put_native_function("shift", shift);
     put_native_function("pop", pop);
     put_native_function("push", push, 1);
+    put_native_function("toString", to_string, 0);
     put("length", Value(0));
 }
 
@@ -45,6 +48,18 @@ ArrayPrototype::~ArrayPrototype()
 {
 }
 
+static Array* array_from(Interpreter& interpreter)
+{
+    auto* this_object = interpreter.this_value().to_object(interpreter.heap());
+    if (!this_object)
+        return {};
+    if (!this_object->is_array()) {
+        interpreter.throw_exception<Error>("TypeError", "Not an Array");
+        return nullptr;
+    }
+    return static_cast<Array*>(this_object);
+}
+
 Value ArrayPrototype::push(Interpreter& interpreter)
 {
     auto* this_object = interpreter.this_value().to_object(interpreter.heap());
@@ -75,4 +90,19 @@ Value ArrayPrototype::shift(Interpreter& interpreter)
     return static_cast<Array*>(this_object)->shift();
 }
 
+Value ArrayPrototype::to_string(Interpreter& interpreter)
+{
+    auto* array = array_from(interpreter);
+    if (!array)
+        return {};
+
+    StringBuilder builder;
+    for (size_t i = 0; i < array->elements().size(); ++i) {
+        if (i != 0)
+            builder.append(',');
+        builder.append(array->elements()[i].to_string());
+    }
+    return js_string(interpreter, builder.to_string());
+}
+
 }
diff --git a/Libraries/LibJS/Runtime/ArrayPrototype.h b/Libraries/LibJS/Runtime/ArrayPrototype.h
index 9828512b610..bed19807a56 100644
--- a/Libraries/LibJS/Runtime/ArrayPrototype.h
+++ b/Libraries/LibJS/Runtime/ArrayPrototype.h
@@ -41,6 +41,7 @@ private:
     static Value push(Interpreter&);
     static Value shift(Interpreter&);
     static Value pop(Interpreter&);
+    static Value to_string(Interpreter&);
 };
 
 }
diff --git a/Libraries/LibJS/Tests/Array.prototype.toString.js b/Libraries/LibJS/Tests/Array.prototype.toString.js
new file mode 100644
index 00000000000..e9ace65d26e
--- /dev/null
+++ b/Libraries/LibJS/Tests/Array.prototype.toString.js
@@ -0,0 +1,9 @@
+try {
+    var a = [1, 2, 3];
+    assert(a.toString() === '1,2,3');
+    assert([].toString() === '');
+    assert([5].toString() === '5');
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}