### Here's a different approach

You could treat each group of `childCategories` as it's own datasource.  Then use the [Multiple Datasets][Multiple Datasets] paradigm to automatically apply a header for child items.

The second parameter to [<code>$.typeahead(options, <i>[*datasets]</i>)</code>][typeahead()] takes an array of datasets. We can convert each set of child elements into it's own dataset like this:



    var dataSources = [];
    $.each(movies, function(index, movieItem) {
        if (movieItem.childCategories) {
            var bloodhoundEngine = createBlounhoud(movieItem.childCategories, 'value');
            var dataSource = {
                name: movieItem.value,
                displayKey: 'value',
                source: bloodhoundEngine.ttAdapter(),
                templates: {
                    header: '<h3 class="typeahead-group">' + movieItem.value + '</h3>'
                }
            };
            dataSources.push(dataSource);
        }
    });

Notice that we've defined a *header template* for items in this datasource. We can style it like this:



    .typeahead-group {
      margin: 0 20px 5px 10px;
      padding: 3px 0;
      border-bottom: 1px solid #ccc;
    }

Elements that were not part of a child group could could all get added as part of a single `ungrouped` datasource:



    var ungrouped = [];
    $.each(movies, function(index, movieItem) {
        if (!movieItem.childCategories) {
            ungrouped.push(movieItem);
        }
    });
    
    function addUngroupedItems() {
        var bloodhoundEngine = createBlounhoud(ungrouped, 'value');
        var dataSource = {
            name: 'ungrouped',
            displayKey: 'value',
            source: bloodhoundEngine.ttAdapter()
        };
        // add to first position of array so it doesn't look like it's part of the group above it
        dataSources.unshift(dataSource);
    };

This solution has the benefit of minimally overriding existing typeahead and bloodhound code while working within the framework to provide grouping functionality.

Also, it provides an intuitive UI for users that might know the name of the name of a child item they're looking for, but don't want to have to click through each category to find it.  Most local searches can trivially search on all fields.


### [Working Demo in jsFiddle][fiddle]

[![screenshot][screenshot]][fiddle-show]



> **Aside**: I would try to avoid modifying the source code  directly.  It makes it very difficult to see where you have made your own modifications.  Instead, try using a CDN for the whole library and writing a plugin or wrapper on top of it.  This will make incoporating future revisions much easier.

[Multiple Datasets]: http://twitter.github.io/typeahead.js/examples/#multiple-datasets

[typeahead()]: https://github.com/twitter/typeahead.js/blob/master/doc/jquery_typeahead.md#jquerytypeaheadoptions-datasets

[fiddle]: http://jsfiddle.net/KyleMit/xk3pscgx/
[fiddle-show]: http://jsfiddle.net/KyleMit/xk3pscgx/show

[screenshot]: http://i.imgur.com/mA9DUn7.png

I am using `twitter typeahead` to show category suggestions which works fine for me. 
 The problem is with the display of sub-categories. If a `category has sub-categories`
 `then expand/collapse icon` is shown along with the suggestion, if the user selects one them the sub-categories has to be shown below it, i have succeeded in the display part but `cannot update the dataset` of typeahead so that when the user selects one the sub-categories it should be displayed in the input. `Please use keyboard on Jsfiddle because i have tried only in keypress`. The following is my json array 


JSFIDDLE [here][1]

    [{
        "id": "38",
        "value": "Entertaintment",
        "parent_id": "27",
        "children": "1",
        "childCategories": [{
            "id": "28",
            "value": "Movies",
            "parent_id": "38"
        }, {
            "id": "29",
            "value": "Sports",
            "parent_id": "38"
        }]
    }, {
        "id": "40",
        "value": "eeen",
        "parent_id": "27",
        "children": "1",
        "childCategories": [{
            "id": "41",
            "value": "een child 1",
            "parent_id": "40"
        }]
    }, {
        "id": "41",
        "value": "een child 1",
        "parent_id": "40",
        "children": "0",
        "childCategories": false
    }]

I have tried the following:

    _onEnterKeyed: function onEnterKeyed(type, $e) {
        var cursorDatum, topSuggestionDatum;
        cursorDatum = this.dropdown.getDatumForCursor();
        topSuggestionDatum = this.dropdown.getDatumForTopSuggestion();
        //My custom condition, if category has children show sub-categories below 
        if (cursorDatum.raw && cursorDatum.raw.children == "1") {
            //below line is my failed try  
	        //this.dropdown.updateChild('',cursorDatum.raw.childCategories,false); 
            var that = this, onSuggestionClick, onSuggestionMouseEnter, onSuggestionMouseLeave;
            var childHTML='';
            $('.ttchild').remove();
            //adding the sub-categories to dropdown
            $.each(cursorDatum.raw.childCategories,function(i,v){
                childHTML += '<div class="tt-suggestion ttchild"><div class="suggestions"><span>'+this.value+'</span></div></div>';
            });
            $(childHTML).insertAfter('.tt-cursor');
            return;
        }

        if (cursorDatum) {
            this._select(cursorDatum);
            $e.preventDefault();
        } 
        else if (this.autoselect && topSuggestionDatum) {
            this._select(topSuggestionDatum);
            $e.preventDefault();
        }
    },

    //This is my custom function trying to update the dataset, but i know its totally wrong.
    updateChild: function updateChild(query,childs) {
        var that = this;
        this.query = query;
        this.canceled = false;
        this.source(query, render);
    		
        function render(childs) {
            if (!that.canceled && query === that.query) {
                that._render(query, childs);
            }
        }
    },


JSFIDDLE [here][2]

e.g: The Entertainment category has subcategories movies and sports.

Hope any one would help me....


  [1]: http://jsfiddle.net/e0zqL2qd/2/
  [2]: http://jsfiddle.net/e0zqL2qd/2/