Showing unique characters in a string only once

Question

I have a string with repeated letters. I want letters that are repeated more than once to show only once. For instance I have a string aaabbbccc i want the result to be abc.

Answer 1

Per the actual question: "if the letter doesn't repeat its not shown"

function unique_char(str)
{
    var obj = new Object();

    for (var i = 0; i < str.length; i++)
    {
        var chr = str[i];
        if (chr in obj)
        {
            obj[chr] += 1;
        }
        else
        {
            obj[chr] = 1;
        }
    }

    var multiples = [];
    for (key in obj)
    {
        // Remove this test if you just want unique chars
        // But still keep the multiples.push(key)
        if (obj[key] > 1)
        {
            multiples.push(key);
        }
    }

    return multiples.join("");
}

var str = "aaabbbccc";
document.write(unique_char(str));