Blog - USING JQUERY TO REFERENCE AN INPUT IN VISUALFORCE

gistfile1.html

<apex:form id="form">
  <apex:pageBlock id="blockContact" mode="edit">
    <apex:pageBlockSection id="blockDetails" title="Details">
      <apex:inputField id="inputContactName" value="{!Contact.Name}" />
    </apex:pageBlockSection>
  </apex:pageBlock>
</apex:form>

gistfile2.xml

<input id="j_id0:form:blockContact:blockDetails:inputContactName" type="text" />

gistfile3.js

var o = document.getElementById('j_id0:form:blockContact:blockDetails:inputContactName');

gistfile4.html

<apex:includeScript value="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js" />
<script type="text/javascript">
j$ = jQuery.noConflict();
j$(document).ready(function() {
  // The dollar sign after the id attribute tells jQuery to return any elements
  // with an id that end in 'ContactName'
  var o = j$('input[id$=ContactName]').val();
});
</script>