Edit in JSFiddle

class AutoCompleter
    constructor: ->
        @trie = {}
    
    add: (word) ->
        root = @trie
        for c in word
            if !root[c]?
                root[c] = {}
            root = root[c]
        
    suggest: (prefix) ->
        root = @trie
        word = ""
        words = []
        for c in prefix
            return word unless root[c]?
            root = root[c]
            word = word + c
        @getWords(root, word, words)
        words
    
    getWords: (root, word, words) ->
        if _.isEmpty(root)
            words.push word
        else
            for key, value of root
                @getWords(value, word + key, words)
    
    autoComplete: ->
        words = @suggest $('#search').val()
        html = """
               <p>Results: </p>
               <ul>
               """
        for w in words
            html += "<li>#{w}</li>"
        html += '</ul>'
        $('#result').html html
        
ac = new AutoCompleter
ac.add 'amy'
ac.add 'ann'
$('button').click -> ac.add $('#word').val()
$('#search').on 'input', -> ac.autoComplete() 
    

<p>Add to Trie:
    <input type="textbox" id='word'></input>
    <button type='button' name='add'>add word</button>
</p>
<p>Search:
    <input type='textbox' id='search' />
</p>
<p>
    <div id='result'></div>
</p>