Prevent insertion of special char on key press, but allow existing ones

I am facing some problems in preventing special chars in a textarea. My problem is how to describe below

I have an auto full textbox for multiple names and each name is comma separated (this is a requirement).

for example: Riki, jumjum, lima, Parth

My Javascript:

$("#facilitatorId").autocomplete({
    minLength: 1,
    source: function(request, response) {
    if(extractLast(request.term) != "" && extractLast(request.term).length >= 1) {
    $.ajax({
        cache: false,
        type: "GET",
        url: CompetencyWebApiUrl + "EventApi/GetAllUserNames?facilitatorName=" + extractLast(request.term),
        dataType: "json",
        timeout: 10000000,

            success: function(data)
            {
                if (data != null && data.length > 0 && data[0].LogError == null)
                {
                    var arryValue =[];
                    for (var i = 0; i < data.length; i++)
                    {
                        var facilitatorNames = {
                        text: data[i].FirstName + " " + data[i].LastName,
                        value : data[i].FirstName + " " + data[i].LastName
                        }
                        arryValue.push(facilitatorNames)
                    }
                    response(arryValue);
                }
                else
                {
                    $(".ui-autocomplete").css("display", "none");
                }   
            },

            error: function (x, t, m)
            {
                if(t == "timeout")
                {
                    $("#errorData").show();
                    $("#errorData").html("service timeout, Please run again");
                }
                else
                {
                    $("#errorData").show();
                    $("#errorData").html("Rating service is unavailable, please try again after some time." + "" + "Error message:" + "" +t);
                }
            }
    });
    } //ends if
},

    focus: function ()
    {
        // prevent value inserted on focus
        return false;
    },
    select: function (event, ui)
    {

        //if its the first value then do not append comma and space before the value
        if (this.value.trim().indexOf(' ') === -1)
        {
            var first = ui.item.text;
            this.value = first + " ";
        }
        //else appends comma and space
        else
        {
            var facilitator = $('#facilitatorId').val().trim();
            var current = facilitator.substring(0, facilitator.lastIndexOf(" "));
            current += ", " + ui.item.text;
            this.value = current + " ";
        }

        return false;
    }
});

      

        
        
        
      

    

And my HTML:

<input type="text" name="Facilitator" id="facilitatorId" onkeyup="Validation(this, event)">

      

        
        
        
      

    

Validation(this, event)

the method only prevents numbers from being entered.

Now I am outputting the code in such a way that if the user tries to enter a special char (such as a comma) textbox

it will not accept the special char, but still it will not remove the existing special characters (the reason names are separated by commas)

Code Validation

:

function Validation(item, evt) {
    var id = item.id;
    var value = item.value.replace(/[0-9]/g, '')
    $('#' + id).val(value);
}