LibJS: Add support for arbitrary arguments to Math.max

Address the FIXME in MathObject::max to handle an arbitrary
number of arguments. Also adding a test case to verify the
behavior of Math.max() while I'm here.

Libraries/LibJS/Runtime/MathObject.cpp

@@ -115,21 +115,16 @@ Value MathObject::max(Interpreter& interpreter)
     if (!interpreter.argument_count()) {
         // FIXME: I think this should return *negative* infinity.
         return js_infinity();
-    }
-
-    if (interpreter.argument_count() == 1)
+    } else if (interpreter.argument_count() == 1) {
         return interpreter.argument(0).to_number();
-
-    if (interpreter.argument_count() == 2) {
-        auto a = interpreter.argument(0).to_number();
-        auto b = interpreter.argument(1).to_number();
-        return Value(a.as_double() > b.as_double() ? a : b);
+    } else {
+        Value max = interpreter.argument(0).to_number();
+        for (size_t i = 1; i < interpreter.argument_count(); ++i) {
+            Value cur = interpreter.argument(i).to_number();
+            max = Value(cur.as_double() > max.as_double() ? cur : max);
+        }
+        return max;
     }
-
-    // FIXME: Support Math.max() with more arguments.
-    ASSERT_NOT_REACHED();
-    return {};
 }
 
-
 }

Libraries/LibJS/Tests/Math.max.js

@@ -0,0 +1,14 @@
+function assert(x) { if (!x) throw 1; }
+
+try {
+    assert(Math.max.length === 2);
+    assert(Math.max(1) === 1);
+    assert(Math.max(2, 1) === 2);
+    assert(Math.max(1, 2, 3) === 3);
+    assert(isNaN(Math.max(NaN)));
+    assert(isNaN(Math.max("String", 1)));
+
+    console.log("PASS");
+} catch {
+    console.log("FAIL");
+}