You can pass event to the function from which you can access the property keyCode.

But I would recommend you to see the documentation before using KeyboardEvent.keyCode

You should avoid using this if possible; it's been deprecated for some time. Instead, you should use KeyboardEvent.code, if it's implemented. Unfortunately, some browsers still don't have it, so you'll have to be careful to make sure you use one which is supported on all target browsers. Google Chrome and Safari have implemented KeyboardEvent.keyIdentifier, which was defined in a draft specification but not the final spec.

function callMyFunction (e, importantothervalue) {
  console.log(e.code);
  console.log(importantothervalue)
}

<textarea onkeyup="callMyFunction(event, 1);"></textarea>
<textarea onkeyup="callMyFunction(event, 2);"></textarea>
<textarea onkeyup="callMyFunction(event, 3);"></textarea>

i'd go with something like this:

$(function () {
    $(document).on('keyup keydown keypress', function (event) {
        if (event.keyCode == 52 && event.shiftKey) {
            alert('foo');
        }
    });
});

jsfiddle

The events are for completely different purposes. Use keyup and keydown for identifying physical keys and keypress for identifying typed characters. The two are fundamentally different tasks with different events; don't try to mix the two. In particular, keyCode on keypress events is usually redundant and shouldn't be used (except in older IE, but see the linked document below for more on that); for printable keypresses it's usually the same as which and charCode, although there is some variation between browsers.

Jan Wolter's article on key events, already linked to in another answer, is the definitive word on this subject for me and has tables describing what each of the different properties returns for each type of key event and each browser.

Your code works for me (see below). Maybe check where you are binding your keyup event. It should be bound once when the document loads before the page shows. If you bind it multiple times (i.e. if the code that contains your keyup function runs more than once) you will run into problems.

$("#arama").on("keyup", function(event) {
  var i = event.keyCode;
  if ((i >= 48 && i <= 57) || (i >= 96 && i <= 105)) {
    $("#arama").off("keyup");
    console.log("Number pressed. Stopping...");
  } else {
    console.log("Non-number pressed.");
  }
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<input id="arama" />

You need to check which key is being pressed ... you are running your function each time ANY key is being pressed right now. Inside your searchCensor() function you will want to have a check like this: if (event.keyCode == 13) {