Iterating through Grid control using javascript

I have a data grid control which has check box as one of its field. What I need to do is to see which of the checkboxes have been checked and then get the corresponding datakey name/value stored as a hidden field, concatenate all these values into a comma seperated string and pass it to a modal window. I need to do all of these inJavascript. Can someone help me with this..

Thanks!!