javascript - jQuery Autocomplete: saving new tags to a database -

i'm noob in kind of field, hope i'll find answer here. i'm trying implement tagging system storing images dabatase. user given chance upload new image, adding little description , (here comes difficult part me) adding tags it. i've found quite documentations aboout using jquery autocomplete read existing tags db. however, need opportunity check if tag exists and, if not, add db. please give me hand on quest?

long story short: need use jquery autocomplete (or equivalent plugin) both "getting from" , "saving to" tags database.

thank you. :)

edit: form i'm planning use insert tags (and description). i've implemented 2 jquery functions limit max number of chars in "description" textarea , max number of words in "tags" one.

<form method="post" action="/upload" accept-charset="utf-8">   <div>     <label>descrizione:</label>     <textarea id="description" maxlength="240"></textarea>     <div id="leftchars"></div>     <hr>     <label>tag:</label>     <textarea id="tags" maxlength="240"></textarea>     <div id="lefttags"></div>   </div>   <br>   <input class="btn btn-default btn-upload" type="button" value="upload" onclick=""> </form> 

i've found answer in comments @ post: select2 . hope in future.