Ajax jquery async return value

This is not possible.
Javascript runs on the UI thread; if your code waits for the server to reply, the browser must remain frozen.

Instead, you need to return the value using a callback:

function get_char_val(merk, callback){      var returnValue = null;    $.ajax({                   type:       "POST",                url:            "char_info2.php",                   data:   { name: merk },                   dataType: "html",                  success:    function(data) {                    callback(data);                }         }); }get_char_val('x', function(px) { ... });get_char_val('y', function(py) { ... });

Note that the two callbacks will run in an unpredictable order.

You should modify your design so that you can get all twenty values in a single AJAX request.
For example, you can take a comma-separated list of values, and return a JSON object like { x: "...", y: "..." }.

You can not make variable assignments this way (async). you must set the variables in the success handler.

variableArray = new Array(); get_char_val('x');get_char_val('y');function get_char_val(merk){      var returnValue = null;    $.ajax({           type:       "POST",        url:            "char_info2.php",           data:   { name: merk },           dataType: "html",          success:    function(data)            {                variableArray[merk] = data;            }     }); }

Once all of the retrievals are finished you can access the x and y variables by using variableArray[x] and variableArray[y]

This may not be what you are expecting but you can set async: true if you dont want pause in the browser and so what you want to do with px on success