function getQueryVariable(variable) {
  var query = window.location.search.substring(1);
  var vars = query.split("&");
  for (var i=0;i<vars.length;i++) {
    var pair = vars[i].split("=");
    if (pair[0] == variable) {
      return decodeURIComponent(pair[1]);
    }
  } 
  return null;
}

例子：

getQueryVariable('key')