asp.net mvc - convert javascript variable to C# variable

Question

I want to use a javascript variable to pass as a parameter to my class constructor in C#.

How can I translate the javascript variable ID to C# such that I am able to pass the value on User.IsOnLeave?

<script type="text/javascript">
  var ID;
  var dateToEvaluate;

  function convertVariable() {
    *if (User.IsOnLeave(***ID***, dateToEvaluate)) {...}*
  }
</script>

Answer 1

You can't access JS variables directly from C#, because JS is client-side and C# is server-side. You can make a controller action and make an AJAX request to it with those parameters. Like this:

JS:

var id;
var dataToEvaluate;

jQuery.ajax({
    type: 'POST',
    url: 'SomeController/SomeAction',
    data: { id: id, dataToEvaluate: dataToEvaluate },
    success: function(data) {
        // do what you have to do with the result of the action
    }
});

controller:

public ActionResult SomeAction(string id, string dataToEvaluate)
{
     // some processing here
     return <probably a JsonResult or something that fits your needs>
}