PHP数组由xmlHttp.responseText转换为JavaScript

This is my PHP code

$cars = array("Volvo", "BMW", "Toyota"); 
echo $cars;

This is my JavaScript

function assign_dt() {
  var cars = xmlHttp.responseText;

    document.getElementById('des').innerHTML = cars;

}

I need the values, but they shows me like this "Array" on the output.

You need to convert the array to a string - use json_encode() for this:

$cars = array("Volvo", "BMW", "Toyota"); 
echo json_encode($cars);