From 6a5cd32205dab3e2764fe59243862e4b9094bc67 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Fri, 27 Mar 2020 12:59:41 +0100
Subject: [PATCH] LibJS: The global isNaN() should coerce to number before
 testing NaN

For stricter NaN checking, we'll have to implement Number.isNaN().
---
 Libraries/LibJS/Runtime/GlobalObject.cpp | 2 +-
 Libraries/LibJS/Tests/NaN-basic.js       | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/Libraries/LibJS/Runtime/GlobalObject.cpp b/Libraries/LibJS/Runtime/GlobalObject.cpp
index c1a344df30..b45fb867ca 100644
--- a/Libraries/LibJS/Runtime/GlobalObject.cpp
+++ b/Libraries/LibJS/Runtime/GlobalObject.cpp
@@ -21,7 +21,7 @@ GlobalObject::GlobalObject()
     put_native_function("isNaN", [](Object*, Vector<Value> arguments) -> Value {
         if (arguments.size() < 1)
             return js_undefined();
-        return Value(arguments[0].is_nan());
+        return Value(arguments[0].to_number().is_nan());
     });
     put("Math", heap().allocate<MathObject>());
 }
diff --git a/Libraries/LibJS/Tests/NaN-basic.js b/Libraries/LibJS/Tests/NaN-basic.js
index 94f271d35e..75ae62f16e 100644
--- a/Libraries/LibJS/Tests/NaN-basic.js
+++ b/Libraries/LibJS/Tests/NaN-basic.js
@@ -5,7 +5,7 @@ try {
     assert(nan + "" == "NaN");
     assert(isNaN(nan) === true);
     assert(isNaN(0) === false);
-    assert(isNaN(undefined) === false);
+    assert(isNaN(undefined) === true);
     assert(isNaN(null) === false);
     console.log("PASS");
 } catch (e) {