function (elem, rs) {
        var rows = [];
        var ix = 0;
        var oldIndex = -1;

        var onMouseOver = function () { this.style.outline = '1px solid #ddd'; }
        var onMouseOut = function () { this.style.outline = '0'; }
        var onMouseDown = function () { p.hide(); p.onmouseselection(this.__hint, p.rs); }

        var p = {
            rs: rs,
            hide: function () {
                elem.style.visibility = 'hidden';
                //rs.hideDropDown();
            },
            refresh: function (token, array) {
                elem.style.visibility = 'hidden';
                ix = 0;
                elem.innerHTML = '';
                var vph = (window.innerHeight || document.documentElement.clientHeight);
                var rect = elem.parentNode.getBoundingClientRect();
                var distanceToTop = rect.top - 6;                        // heuristic give 6px 
                var distanceToBottom = vph - rect.bottom - 6;  // distance from the browser border.

                rows = [];
                for (var i = 0; i < array.length; i++) {

                    if (  (config.caseSensitive && array[i].indexOf(token) !== 0)
                        ||(!config.caseSensitive && array[i].toLowerCase().indexOf(token.toLowerCase()) !== 0)) { continue; }

                    var divRow = document.createElement('div');
                    divRow.className = 'item';
                    //divRow.style.color = config.color;
                    divRow.onmouseover = onMouseOver;
                    divRow.onmouseout = onMouseOut;
                    divRow.onmousedown = onMouseDown;
                    divRow.__hint = array[i];
                    divRow.innerHTML = array[i].substring(0, token.length) + '<b>' + array[i].substring(token.length) + '</b>';
                    rows.push(divRow);
                    elem.appendChild(divRow);
                }
                if (rows.length === 0) {
                    return; // nothing to show.
                }
                if (rows.length === 1 && (   (token.toLowerCase() === rows[0].__hint.toLowerCase() && !config.caseSensitive) 
                                           ||(token === rows[0].__hint && config.caseSensitive))){
                    return; // do not show the dropDown if it has only one element which matches what we have just displayed.
                }

                if (rows.length < 2) return;
                p.highlight(0);

                if (distanceToTop > distanceToBottom * 3) {        // Heuristic (only when the distance to the to top is 4 times more than distance to the bottom
                    elem.style.maxHeight = distanceToTop + 'px';  // we display the dropDown on the top of the input text
                    elem.style.top = '';
                    elem.style.bottom = '100%';
                } else {
                    elem.style.top = '100%';
                    elem.style.bottom = '';
                    elem.style.maxHeight = distanceToBottom + 'px';
                }
                elem.style.visibility = 'visible';
            },
            highlight: function (index) {
                if (oldIndex != -1 && rows[oldIndex]) {
                    rows[oldIndex].className = "item";
                }
                rows[index].className = "item hover"; 
                oldIndex = index;
            },
            move: function (step) { // moves the selection either up or down (unless it's not possible) step is either +1 or -1.
                if (elem.style.visibility === 'hidden') return ''; // nothing to move if there is no dropDown. (this happens if the user hits escape and then down or up)
                if (ix + step === -1 || ix + step === rows.length) return rows[ix].__hint; // NO CIRCULAR SCROLLING. 
                ix += step;
                p.highlight(ix);
                return rows[ix].__hint;//txtShadow.value = uRows[uIndex].__hint ;
            },
            onmouseselection: function () { } // it will be overwritten. 
        };
        return p;
    }
function (elem, rs) {
        var rows = [];
        var ix = 0;
        var oldIndex = -1;

        var onMouseOver = function () { this.style.outline = '1px solid #ddd'; }
        var onMouseOut = function () { this.style.outline = '0'; }
        var onMouseDown = function () { p.hide(); p.onmouseselection(this.__hint, p.rs); }

        var p = {
            rs: rs,
            hide: function () {
                elem.style.visibility = 'hidden';
                
            },
            refresh: function (token, array) {
                elem.style.visibility = 'hidden';
                ix = 0;
                elem.innerHTML = '';
                var vph = (window.innerHeight || document.documentElement.clientHeight);
                var rect = elem.parentNode.getBoundingClientRect();
                var distanceToTop = rect.top - 6;                        
                var distanceToBottom = vph - rect.bottom - 6;  

                rows = [];
                for (var i = 0; i < array.length; i++) {

                    if (  (config.caseSensitive && array[i].indexOf(token) !== 0)
                        ||(!config.caseSensitive && array[i].toLowerCase().indexOf(token.toLowerCase()) !== 0)) { continue; }

                    var divRow = document.createElement('div');
                    divRow.className = 'item';
                    
                    divRow.onmouseover = onMouseOver;
                    divRow.onmouseout = onMouseOut;
                    divRow.onmousedown = onMouseDown;
                    divRow.__hint = array[i];
                    divRow.innerHTML = array[i].substring(0, token.length) + '<b>' + array[i].substring(token.length) + '</b>';
                    rows.push(divRow);
                    elem.appendChild(divRow);
                }
                if (rows.length === 0) {
                    return; 
                }
                if (rows.length === 1 && (   (token.toLowerCase() === rows[0].__hint.toLowerCase() && !config.caseSensitive) 
                                           ||(token === rows[0].__hint && config.caseSensitive))){
                    return; 
                }

                if (rows.length < 2) return;
                p.highlight(0);

                if (distanceToTop > distanceToBottom * 3) {        
                    elem.style.maxHeight = distanceToTop + 'px';  
                    elem.style.top = '';
                    elem.style.bottom = '100%';
                } else {
                    elem.style.top = '100%';
                    elem.style.bottom = '';
                    elem.style.maxHeight = distanceToBottom + 'px';
                }
                elem.style.visibility = 'visible';
            },
            highlight: function (index) {
                if (oldIndex != -1 && rows[oldIndex]) {
                    rows[oldIndex].className = "item";
                }
                rows[index].className = "item hover"; 
                oldIndex = index;
            },
            move: function (step) { 
                if (elem.style.visibility === 'hidden') return ''; 
                if (ix + step === -1 || ix + step === rows.length) return rows[ix].__hint; 
                ix += step;
                p.highlight(ix);
                return rows[ix].__hint;
            },
            onmouseselection: function () { } 
        };
        return p;
    }
function ( elem , rs ) { var rows = [ ] ; var ix = 0 ; var oldIndex = - 1 ; var onMouseOver = function ( ) { this . style . outline = '1px solid #ddd' ; } var onMouseOut = function ( ) { this . style . outline = '0' ; } var onMouseDown = function ( ) { p . hide ( ) ; p . onmouseselection ( this . __hint , p . rs ) ; } var p = { rs : rs , hide : function ( ) { elem . style . visibility = 'hidden' ; //rs.hideDropDown(); } , refresh : function ( token , array ) { elem . style . visibility = 'hidden' ; ix = 0 ; elem . innerHTML = '' ; var vph = ( window . innerHeight || document . documentElement . clientHeight ) ; var rect = elem . parentNode . getBoundingClientRect ( ) ; var distanceToTop = rect . top - 6 ; // heuristic give 6px  var distanceToBottom = vph - rect . bottom - 6 ; // distance from the browser border. rows = [ ] ; for ( var i = 0 ; i < array . length ; i ++ ) { if ( ( config . caseSensitive && array [ i ] . indexOf ( token ) !== 0 ) || ( ! config . caseSensitive && array [ i ] . toLowerCase ( ) . indexOf ( token . toLowerCase ( ) ) !== 0 ) ) { continue ; } var divRow = document . createElement ( 'div' ) ; divRow . className = 'item' ; //divRow.style.color = config.color; divRow . onmouseover = onMouseOver ; divRow . onmouseout = onMouseOut ; divRow . onmousedown = onMouseDown ; divRow . __hint = array [ i ] ; divRow . innerHTML = array [ i ] . substring ( 0 , token . length ) + '<b>' + array [ i ] . substring ( token . length ) + '</b>' ; rows . push ( divRow ) ; elem . appendChild ( divRow ) ; } if ( rows . length === 0 ) { return ; // nothing to show. } if ( rows . length === 1 && ( ( token . toLowerCase ( ) === rows [ 0 ] . __hint . toLowerCase ( ) && ! config . caseSensitive ) || ( token === rows [ 0 ] . __hint && config . caseSensitive ) ) ) { return ; // do not show the dropDown if it has only one element which matches what we have just displayed. } if ( rows . length < 2 ) return ; p . highlight ( 0 ) ; if ( distanceToTop > distanceToBottom * 3 ) { // Heuristic (only when the distance to the to top is 4 times more than distance to the bottom elem . style . maxHeight = distanceToTop + 'px' ; // we display the dropDown on the top of the input text elem . style . top = '' ; elem . style . bottom = '100%' ; } else { elem . style . top = '100%' ; elem . style . bottom = '' ; elem . style . maxHeight = distanceToBottom + 'px' ; } elem . style . visibility = 'visible' ; } , highlight : function ( index ) { if ( oldIndex != - 1 && rows [ oldIndex ] ) { rows [ oldIndex ] . className = "item" ; } rows [ index ] . className = "item hover" ; oldIndex = index ; } , move : function ( step ) { // moves the selection either up or down (unless it's not possible) step is either +1 or -1. if ( elem . style . visibility === 'hidden' ) return '' ; // nothing to move if there is no dropDown. (this happens if the user hits escape and then down or up) if ( ix + step === - 1 || ix + step === rows . length ) return rows [ ix ] . __hint ; // NO CIRCULAR SCROLLING.  ix += step ; p . highlight ( ix ) ; return rows [ ix ] . __hint ; //txtShadow.value = uRows[uIndex].__hint ; } , onmouseselection : function ( ) { } // it will be overwritten.  } ; return p ; }
<-- it will contain the leftSide part of the textfield (the bit that was already autocompleted)
< -- it will contain the leftSide part of the textfield ( the bit that was already autocompleted )