diff --git a/src/main/java/me/topchetoeu/jscript/runtime/SimpleRepl.java b/src/main/java/me/topchetoeu/jscript/runtime/SimpleRepl.java
index 2075db9..0a6da34 100644
--- a/src/main/java/me/topchetoeu/jscript/runtime/SimpleRepl.java
+++ b/src/main/java/me/topchetoeu/jscript/runtime/SimpleRepl.java
@@ -383,6 +383,15 @@ public class SimpleRepl {
             }
             System.out.println();
 
+            return Value.UNDEFINED;
+        }));
+        glob.defineOwnMember(null, "measure", new NativeFunction("measure", args -> {
+            var start = System.nanoTime();
+
+            ((FunctionValue)args.get(0)).invoke(args.env, Value.UNDEFINED);
+
+            System.out.println(String.format("Finished in %sns", System.nanoTime() - start));
+
             return Value.UNDEFINED;
         }));
     }
diff --git a/src/main/java/me/topchetoeu/jscript/runtime/values/Value.java b/src/main/java/me/topchetoeu/jscript/runtime/values/Value.java
index 1497fb2..7ad0c4c 100644
--- a/src/main/java/me/topchetoeu/jscript/runtime/values/Value.java
+++ b/src/main/java/me/topchetoeu/jscript/runtime/values/Value.java
@@ -522,6 +522,7 @@ public abstract class Value {
         else if (this instanceof VoidValue) return ((VoidValue)this).name;
         else if (this instanceof StringValue) return JSON.stringify(JSONElement.string(((StringValue)this).value));
         else if (this instanceof SymbolValue) return this.toString();
+        else if (this instanceof NumberValue num && num.isLong()) return num.getLong() + "i";
         else return this.toString(env);
     }
 
diff --git a/src/main/java/me/topchetoeu/jscript/runtime/values/primitives/numbers/IntValue.java b/src/main/java/me/topchetoeu/jscript/runtime/values/primitives/numbers/IntValue.java
index 0e10367..9d90a75 100644
--- a/src/main/java/me/topchetoeu/jscript/runtime/values/primitives/numbers/IntValue.java
+++ b/src/main/java/me/topchetoeu/jscript/runtime/values/primitives/numbers/IntValue.java
@@ -4,7 +4,7 @@ public final class IntValue extends NumberValue {
     public final long value;
 
     @Override public boolean isInt() {
-        return (value & 0xFFFFFFFF00000000l) == 0;
+        return (int)value == value;
     }
     @Override public boolean isLong() {
         return true;