JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.4/themes/ui-lightness/jquery-ui.css">
<div rel="one"></div>
<div rel="one"></div>
<div rel="two"></div>
<div rel="one"></div>
<div rel="three"></div>
<div rel="three"></div>
<div rel="one"></div>

JavaScript

$.grep = function( elems, callback, inv ) {
    var ret = [], retVal;
    inv = !!inv;

    // Go through the array, only saving the items
    // that pass the validator function
    for ( var i = 0, length = elems.length; i < length; i++ ) {
        
        // added new Array as arg------------v
        retVal = !!callback( elems[ i ], i, ret );
        if ( inv !== retVal ) {
            ret.push( elems[ i ] );
        }
    }

    return ret;
};


var arr = 
$.grep(
    $('div').map(function() { return $(this).attr('rel'); } ).get(),
    function( v, i, arr ) { return $.inArray( v, arr ) === -1; } // exclude dupes
);

document.write( arr );