LibJS: Implement Number.isNaN()

Like the global isNaN() without the number coercion.

Libraries/LibJS/Runtime/GlobalObject.cpp

@@ -138,8 +138,7 @@ Value GlobalObject::gc(Interpreter& interpreter)
 
 Value GlobalObject::is_nan(Interpreter& interpreter)
 {
-    auto value = interpreter.argument(0).to_number();
-    return Value(value.is_nan());
+    return Value(interpreter.argument(0).to_number().is_nan());
 }
 
 Value GlobalObject::is_finite(Interpreter& interpreter)

Libraries/LibJS/Runtime/NumberConstructor.cpp

@@ -41,6 +41,7 @@ NumberConstructor::NumberConstructor()
     : NativeFunction("Number", *interpreter().global_object().function_prototype())
 {
     put_native_function("isFinite", is_finite, 1);
+    put_native_function("isNaN", is_nan, 1);
     put_native_function("isSafeInteger", is_safe_integer, 1);
 
     put("prototype", interpreter().global_object().number_prototype());
@@ -79,6 +80,11 @@ Value NumberConstructor::is_finite(Interpreter& interpreter)
     return Value(interpreter.argument(0).is_finite_number());
 }
 
+Value NumberConstructor::is_nan(Interpreter& interpreter)
+{
+    return Value(interpreter.argument(0).is_nan());
+}
+
 Value NumberConstructor::is_safe_integer(Interpreter& interpreter)
 {
     if (!interpreter.argument(0).is_number())

Libraries/LibJS/Runtime/NumberConstructor.h

@@ -43,6 +43,7 @@ private:
     virtual const char* class_name() const override { return "NumberConstructor"; }
 
     static Value is_finite(Interpreter&);
+    static Value is_nan(Interpreter&);
     static Value is_safe_integer(Interpreter&);
 };
 

Libraries/LibJS/Tests/Number.isNaN.js

@@ -0,0 +1,30 @@
+load("test-common.js");
+
+try {
+    assert(Number.isNaN.length === 1);
+
+    assert(Number.isNaN(0) === false);
+    assert(Number.isNaN(42) === false);
+    assert(Number.isNaN("") === false);
+    assert(Number.isNaN("0") === false);
+    assert(Number.isNaN("42") === false);
+    assert(Number.isNaN(true) === false);
+    assert(Number.isNaN(false) === false);
+    assert(Number.isNaN(null) === false);
+    assert(Number.isNaN([]) === false);
+    assert(Number.isNaN(Infinity) === false);
+    assert(Number.isNaN(-Infinity) === false);
+    assert(Number.isNaN() === false);
+    assert(Number.isNaN(undefined) === false);
+    assert(Number.isNaN("foo") === false);
+    assert(Number.isNaN({}) === false);
+    assert(Number.isNaN([1, 2, 3]) === false);
+
+    assert(Number.isNaN(NaN) === true);
+    assert(Number.isNaN(Number.NaN) === true);
+    assert(Number.isNaN(0 / 0) === true);
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e.message);
+}