How do I write a jquery function that accepts a callback as a parameter

function ChangeDasPanel(controllerPath, postParams, f) {
  $.get(
    controllerPath, 
    postParams, 
    function(returnValue) {
      var $DasSpace = $('#DasSpace');
      $DasSpace.hide(
        "slide", { direction: "right" }, 1000, 
        function() {
          $DasSpace.contents().remove();
          $DasSpace.append(returnValue).css("display", "block");
          $DasSpace.show("slide", { direction: "right" }, 1000);
        }
      );
      if (typeof f == "function") f(); else alert('meh');
    }
  );
};

You can pass functions like any other object in JavaScript. Passing in a callback function is straight-forward, you even do it yourself in the $.post() call.

You can decide whether you want to have your callback called as part of the $.post() callback or on its own.

You know that global variables and functions are evil, so why not put your's into the jQuery namespace:

$.extend({
  myFunc : function(someArg, callbackFnk){
    var url = "http://example.com?q=" + someArg;
    $.getJSON(url, function(data){

      // now we are calling our own callback function
      if(typeof callbackFnk == 'function'){
        callbackFnk.call(this, data);
      }

    });
  }
});

$.myFunc(args, function(){
  // now my function is not hardcoded
  // in the plugin itself
});

Read this post to get a better understanding: Creating callback functions in jQuery

If I understand you correctly, it's as easy as setting another parameter and calling the variable as a function:

function foo(mycallback) {
    mycallback();
}

Why don't you use an object that you can pass through to the function. It is much more jQuery like and it saves you having x named parameters which is hard to maintain as it can get unwieldy when you get past 3 params.

e.g

function callingFunction(){

      var fnSettings: {
        url: someUrl,
        data: params,
        callback : function(){}
      };


      yourFunction( fnSettings );

}

function yourFunction( settings ) {

      $.post( settings.url, settings.data, settings.callback );

}