getting url params with coffeescript and jquery

get_url_params.js.coffee

# Returns get parameters.
#
# If the desired param does not exist, null will be returned
#
# To get the document params:
# @example value = $(document).getUrlParam("paramName");
#
# To get the params of a html-attribut (uses src attribute)
# @example value = $('#imgLink').getUrlParam("paramName");
jQuery.fn.extend
  getUrlParam: (strParamName) ->
    strParamName = escape(unescape(strParamName))

    if $(this).attr("nodeName") is "#document"
      if window.location.search.search(strParamName) > -1
        qString = window.location.search.substr(1,window.location.search.length).split("&")
    else if $(this).attr("src") isnt "undefined"
      strHref = $(this).attr("src")
      if strHref.indexOf("?") > -1
        strQueryString = strHref.substr(strHref.indexOf("?") + 1)
        qString = strQueryString.split("&")
    else if $(this).attr("href") isnt "undefined"
      strHref = $(this).attr("href")
      if strHref.indexOf("?") > -1
        strQueryString = strHref.substr(strHref.indexOf("?") + 1)
        qString = strQueryString.split("&")
    else
      return null

    return null unless qString

    returnVal = (query.split("=")[1] for query in qString when escape(unescape(query.split("=")[0])) is strParamName)

    if returnVal.lenght is 0
      null
    else if returnVal.lenght is 1
      returnVal[0]
    else
      returnVal