LibJS: Implement most of the Reflect object

Author: https://github.com/linusg
Commit: 79b829637e
Pull-request: https://github.com/SerenityOS/serenity/pull/2047
Reviewed-by: https://github.com/awesomekling

Libraries/LibJS/Tests/Reflect.construct.js

@@ -0,0 +1,54 @@
+load("test-common.js");
+
+try {
+    assert(Reflect.construct.length === 2);
+
+    [null, undefined, "foo", 123, NaN, Infinity].forEach(value => {
+        assertThrowsError(() => {
+            Reflect.construct(value);
+        }, {
+            error: TypeError,
+            message: "First argument of Reflect.construct() must be a function"
+        });
+
+        assertThrowsError(() => {
+            Reflect.construct(() => {}, value);
+        }, {
+            error: TypeError,
+            message: "Arguments list must be an object"
+        });
+
+        assertThrowsError(() => {
+            Reflect.construct(() => {}, [], value);
+        }, {
+            error: TypeError,
+            message: "Optional third argument of Reflect.construct() must be a constructor"
+        });
+    });
+
+    var a = Reflect.construct(Array, [5]);
+    assert(a instanceof Array);
+    assert(a.length === 5);
+
+    var s = Reflect.construct(String, [123]);
+    assert(s instanceof String);
+    assert(s.length === 3);
+    assert(s.toString() === "123");
+
+    function Foo() {
+        this.name = "foo";
+    }
+    
+    function Bar() {
+        this.name = "bar";
+    }
+
+    var o = Reflect.construct(Foo, [], Bar);
+    assert(o.name === "foo");
+    assert(o instanceof Foo === false);
+    assert(o instanceof Bar === true);
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}