getting values from formtext using plugins

hello guys i'm tryin to write a plugging form my omeka website that consist to make an autocomplete using javascript and i dont know how to get the value that user types in the text form in the search item page

<div id="search-keywords" class="field">
<div class="two columns alpha">
<?php echo $this->formLabel('keyword-search', __('Search for Keywords')); ?>
<div class="five columns omega inputs">
echo $this->formText(
array('id' => 'keyword-search', 'size' => '40')
thanks for the help