LibJS: Add Array.prototype.toLocaleString()

Author: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/1dd44210b78
Pull-request: https://github.com/SerenityOS/serenity/pull/2431
Reviewed-by: https://github.com/awesomekling ✅

Libraries/LibJS/Runtime/ArrayPrototype.cpp

@@ -53,6 +53,7 @@ ArrayPrototype::ArrayPrototype()
     define_native_function("push", push, 1, attr);
     define_native_function("shift", shift, 0, attr);
     define_native_function("toString", to_string, 0, attr);
+    define_native_function("toLocaleString", to_locale_string, 0, attr);
     define_native_function("unshift", unshift, 1, attr);
     define_native_function("join", join, 1, attr);
     define_native_function("concat", concat, 1, attr);
@@ -264,6 +265,37 @@ Value ArrayPrototype::to_string(Interpreter& interpreter)
     return interpreter.call(join_function.as_function(), this_object);
 }
 
+Value ArrayPrototype::to_locale_string(Interpreter& interpreter)
+{
+    auto* this_object = interpreter.this_value().to_object(interpreter);
+    if (!this_object)
+        return {};
+    String separator = ",";  // NOTE: This is implementation-specific.
+    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(i).value_or(js_undefined());
+        if (interpreter.exception())
+            return {};
+        if (value.is_undefined() || value.is_null())
+            continue;
+        auto* value_object = value.to_object(interpreter);
+        ASSERT(value_object);
+        auto locale_string_result = value_object->invoke("toLocaleString");
+        if (interpreter.exception())
+            return {};
+        auto string = locale_string_result.to_string(interpreter);
+        if (interpreter.exception())
+            return {};
+        builder.append(string);
+    }
+    return js_string(interpreter, builder.to_string());
+}
+
 Value ArrayPrototype::join(Interpreter& interpreter)
 {
     auto* this_object = interpreter.this_value().to_object(interpreter);

Libraries/LibJS/Runtime/ArrayPrototype.h

@@ -46,6 +46,7 @@ private:
     static Value push(Interpreter&);
     static Value shift(Interpreter&);
     static Value to_string(Interpreter&);
+    static Value to_locale_string(Interpreter&);
     static Value unshift(Interpreter&);
     static Value join(Interpreter&);
     static Value concat(Interpreter&);

Libraries/LibJS/Tests/Array.prototype.toLocaleString.js

@@ -0,0 +1,24 @@
+load("test-common.js");
+
+try {
+    assert(Array.prototype.toLocaleString.length === 0);
+
+    assert([].toLocaleString() === "");
+    assert(["foo"].toLocaleString() === "foo");
+    assert(["foo", "bar"].toLocaleString() === "foo,bar");
+    assert(["foo", undefined, "bar", null, "baz"].toLocaleString() === "foo,,bar,,baz");
+
+    var toStringCalled = 0;
+    var o = {
+        toString: () => {
+            toStringCalled++;
+            return "o";
+        }
+    };
+    assert([o, undefined, o, null, o].toLocaleString() === "o,,o,,o");
+    assert(toStringCalled === 3);
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}