LibJS: Make Array.prototype.{join,toString}() generic

Libraries/LibJS/Runtime/ArrayPrototype.cpp

@@ -35,6 +35,7 @@
 #include <LibJS/Runtime/Function.h>
 #include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/MarkedValueList.h>
+#include <LibJS/Runtime/ObjectPrototype.h>
 #include <LibJS/Runtime/Value.h>
 
 namespace JS {
@@ -240,46 +241,48 @@ Value ArrayPrototype::shift(Interpreter& interpreter)
     return array->elements().take_first().value_or(js_undefined());
 }
 
-static Value join_array_with_separator(Interpreter& interpreter, const Array& array, StringView separator)
-{
-    StringBuilder builder;
-    for (size_t i = 0; i < array.elements().size(); ++i) {
-        if (i != 0)
-            builder.append(separator);
-        auto value = array.elements()[i];
-        if (!value.is_empty() && !value.is_undefined() && !value.is_null()) {
-            auto string = value.to_string(interpreter);
-            if (interpreter.exception())
-                return {};
-            builder.append(string);
-        }
-    }
-    return js_string(interpreter, builder.to_string());
-}
-
 Value ArrayPrototype::to_string(Interpreter& interpreter)
 {
-    auto* array = array_from(interpreter);
-    if (!array)
+    auto* this_object = interpreter.this_value().to_object(interpreter);
+    if (!this_object)
         return {};
-
-    return join_array_with_separator(interpreter, *array, ",");
+    auto join_function = this_object->get("join");
+    if (interpreter.exception())
+        return {};
+    if (!join_function.is_function())
+        return ObjectPrototype::to_string(interpreter);
+    return interpreter.call(join_function.as_function(), this_object);
 }
 
 Value ArrayPrototype::join(Interpreter& interpreter)
 {
-    auto* array = array_from(interpreter);
-    if (!array)
+    auto* this_object = interpreter.this_value().to_object(interpreter);
+    if (!this_object)
         return {};
-
     String separator = ",";
     if (interpreter.argument_count()) {
         separator = interpreter.argument(0).to_string(interpreter);
         if (interpreter.exception())
             return {};
     }
-
-    return join_array_with_separator(interpreter, *array, separator);
+    auto length = get_length(interpreter, *this_object);
+    if (interpreter.exception())
+        return {};
+    StringBuilder builder;
+    for (size_t i = 0; i < length; ++i) {
+        if (i > 0)
+            builder.append(separator);
+        auto value = this_object->get_by_index(i).value_or(js_undefined());
+        if (interpreter.exception())
+            return {};
+        if (value.is_undefined() || value.is_null())
+            continue;
+        auto string = value.to_string(interpreter);
+        if (interpreter.exception())
+            return {};
+        builder.append(string);
+    }
+    return js_string(interpreter, builder.to_string());
 }
 
 Value ArrayPrototype::concat(Interpreter& interpreter)

Libraries/LibJS/Runtime/ObjectPrototype.h

@@ -37,12 +37,14 @@ public:
 
     virtual ~ObjectPrototype() override;
 
+    // public to serve as intrinsic function %Object.prototype.toString%
+    static Value to_string(Interpreter&);
+
 private:
     virtual const char* class_name() const override { return "ObjectPrototype"; }
 
     static Value has_own_property(Interpreter&);
     static Value value_of(Interpreter&);
-    static Value to_string(Interpreter&);
 };
 
 }

Libraries/LibJS/Tests/Array.prototype-generic-functions.js

@@ -27,6 +27,22 @@ try {
         assert(o.length === 0);
     });
 
+    {
+        assert(Array.prototype.join.call({}) === "");
+        assert(Array.prototype.join.call({ length: "foo" }) === "");
+        assert(Array.prototype.join.call({ length: 3 }) === ",,");
+        assert(Array.prototype.join.call({ length: 2, 0: "foo", 1: "bar" }) === "foo,bar");
+        assert(Array.prototype.join.call({ length: 2, 0: "foo", 1: "bar", 2: "baz" }) === "foo,bar");
+        assert(Array.prototype.join.call({ length: 3, 1: "bar" }, "~") === "~bar~");
+        assert(Array.prototype.join.call({ length: 3, 0: "foo", 1: "bar", 2: "baz" }, "~") === "foo~bar~baz");
+    }
+
+    {
+        assert(Array.prototype.toString.call({}) === "[object Object]");
+        assert(Array.prototype.toString.call({ join: "foo" }) === "[object Object]");
+        assert(Array.prototype.toString.call({ join: () => "foo" }) === "foo");
+    }
+
     const o = { length: 5, 0: "foo", 1: "bar", 3: "baz" };
 
     {