Java Script Object vs Array

<!DOCTYPE html>
<html>
<head>
</head>
<body>
<h2>JavaScript Objects</h2>
<script>
var plane= {
  type:"MS", 
  model:2001, 
  color:"white"
}
var propertyValues=Object.keys(plane);  
document.write(propertyValues);  

</script>

</body>
</html>