Javascript: Add values to CSV if not in CSV - if Already in CSV - remove from CSV

I am building a CSV string - so everything a user clicks a div - a开发者_JAVA技巧 string of 5 characters gets passed into a hidden field - what I am trying to do is to append each new value and create a CSV string - when done - display in a textbox - if the value being passed into the CSV already exists - remove it and then, just like before, display CSV in the textfield. I have the below, but it just does not work...

function newQuery(val, id) {

    var xy = document.getElementById(id);
    var x = parent.document.getElementById('txtCriteria');
    var myValue = parent.document.getElementById('txtCriteria').value;
    var hdn = document.getElementById("hdnSearch");
    hdn.value += "," + val;

    var element = hdn.value;
    var fin;

    var leadingComma = element.substring(1, 0).toLowerCase();
    var trailingComma = element.substring(element.length - 1);


    // Check for leading comma
    if (leadingComma == ",") {
        fin = element.substring(1);
    }
    // Check for trailing comma
    if (element.charAt(element.length - 1) == ",") {
        fin = element.slice(0, -1);
    }

    if (x.value.search(val) == 0) {
        alert('Already exists');

        fin.replace(val, "");
        x.value = fin;

        // Set image to checked
        xy.src = 'bullet_plus.png';

    }
    else if (element.search(val) > 0) {
        alert('New Selection: ' + fin);

        x.value = fin;

        // Set image to checked
        xy.src = 'bullet_tick.png';

    }
}

When handling CSV I recommend you use Array.join and String.split

var foo = "hello, there, so";
var arr = foo.split(","); // ["hello", " there", "so"];
var bar = arr.join(","); // "hello, there, so"

As for your code it makes little sense without the HTML or without having useful variable names.

A set data structure eliminates a lot of unnecessary work:

function CsvSet(str) {
    var set = {};
    var arr = str.split(",");
    for (var i = 0; i < arr.length; i++)
        set[arr[i]] = true;
    this.set = set;
}

CsvSet.prototype.put = function(val) {
    this.set[val] = !this.set[val];
}

CsvSet.prototype.toString = function() {
    var res = [];
    for (var val in this.set) {
        if (this.set[val])
            res.push(val);
    }
    return res.join();
}

Now let's add and remove some items:

var set = new CsvSet("one,two,three");
set.put("one"); // remove
set.put("seven"); // add
set.toString();

Output:

"two,three,seven"