From 7725b1970e5b7a9ee1e23331f3e19989f28fd03a Mon Sep 17 00:00:00 2001
From: Kesse Jones <kjonesfc@outlook.com>
Date: Thu, 16 Apr 2020 11:35:13 -0300
Subject: [PATCH] LibJS: Add String.prototype.concat

---
 Libraries/LibJS/Runtime/StringPrototype.cpp   | 19 ++++++++++++++++
 Libraries/LibJS/Runtime/StringPrototype.h     |  1 +
 .../LibJS/Tests/String.prototype.concat.js    | 22 +++++++++++++++++++
 3 files changed, 42 insertions(+)
 create mode 100644 Libraries/LibJS/Tests/String.prototype.concat.js

diff --git a/Libraries/LibJS/Runtime/StringPrototype.cpp b/Libraries/LibJS/Runtime/StringPrototype.cpp
index 453e10230d..560cbb3084 100644
--- a/Libraries/LibJS/Runtime/StringPrototype.cpp
+++ b/Libraries/LibJS/Runtime/StringPrototype.cpp
@@ -55,6 +55,7 @@ StringPrototype::StringPrototype()
     put_native_function("trim", trim, 0);
     put_native_function("trimStart", trim_start, 0);
     put_native_function("trimEnd", trim_end, 0);
+    put_native_function("concat", concat, 1);
 }
 
 StringPrototype::~StringPrototype()
@@ -307,4 +308,22 @@ Value StringPrototype::trim_end(Interpreter& interpreter)
     return trim_string(interpreter, *this_object, TrimMode::Right);
 }
 
+Value StringPrototype::concat(Interpreter& interpreter)
+{
+    auto* this_object = interpreter.this_value().to_object(interpreter.heap());
+    if (!this_object)
+        return {};
+    auto& string = this_object->to_string().as_string()->string();
+
+    StringBuilder builder;
+    builder.append(string);
+
+    for (size_t i = 0; i < interpreter.argument_count(); ++i) {
+        auto string_argument = interpreter.argument(i).to_string();
+        builder.append(string_argument);
+    }
+
+    return js_string(interpreter, builder.to_string());
+}
+
 }
diff --git a/Libraries/LibJS/Runtime/StringPrototype.h b/Libraries/LibJS/Runtime/StringPrototype.h
index f9e5b12b43..76f5a0c70c 100644
--- a/Libraries/LibJS/Runtime/StringPrototype.h
+++ b/Libraries/LibJS/Runtime/StringPrototype.h
@@ -53,6 +53,7 @@ private:
     static Value trim(Interpreter&);
     static Value trim_start(Interpreter&);
     static Value trim_end(Interpreter&);
+    static Value concat(Interpreter&);
 };
 
 }
diff --git a/Libraries/LibJS/Tests/String.prototype.concat.js b/Libraries/LibJS/Tests/String.prototype.concat.js
new file mode 100644
index 0000000000..aee254ba71
--- /dev/null
+++ b/Libraries/LibJS/Tests/String.prototype.concat.js
@@ -0,0 +1,22 @@
+load("test-common.js");
+
+try {
+    assert(String.prototype.concat.length === 1);
+    assert("".concat(1) === "1");
+    assert("".concat(3,2,1) === "321");
+    assert("hello".concat(" ", "friends") === "hello friends");
+    assert("".concat(null) === "null");
+    assert("".concat(false) === "false");
+    assert("".concat(true) === "true");
+    assert("".concat([]) === "");
+    assert("".concat([1, 2, 3, 'hello']) === "1,2,3,hello");
+    assert("".concat(true, []) === "true");
+    assert("".concat(true, false) === "truefalse");
+    assert("".concat({}) === "[object Object]");
+    assert("".concat(1, {}) === "1[object Object]");
+    assert("".concat(1, {}, false) === "1[object Object]false");
+
+    console.log("PASS");
+} catch (err) {
+    console.log("FAIL: " + err);
+}