Tim's Code read

code_read.js

function render_servers(environment_name) {
  //  ... 

  jQuery.getJSON(url, function(data) {
   
    // you are using val as your incoming variable here, and also below
    // $.each(data.servers, function(key, val) {
    $.each(data.servers, function(server_name, server_data) {

      // why are you using var $var_name here?  $ is either for mechanically generated code/vars or
      // for jquery selectors:   var $my_buttons = $(".buttons")   
      // no big deal, but javascripters would be all wtf... 
      var $server_id = server_data.id;

      // you are using this as a true/false - just make it a boolean
      var checked=false;  // var checked = ''; 
                        
      searching_for = $("#application_name").val().replace(/[_]/g, "")) // this is expensive(ish)

      jQuery.getJSON(server_instances_url, function(data) {

        // using val here.. i also vote for being more explicit and avoid scoping errors or questions
        $.each(data.instances, function(instance_name, instance_data) {
          if(instance_data.parent_application_name === searching_for) {
            checked = true;  // we found it!!!
          }
        });
      });
      alert(checked);

      // BUG!!! BUG!!!!!
      // you are declaring input inside the block, which means this value WILL NOT get outside of the block!!!!
      var my_cool_input = "";
      if(checked) {          // } else if(checked.match("checked")) {
        var my_cool_input = "i was checked!!";
        var $input = "<input " + checked + " class='server_checkbox' id=" + val.id + " name=servers[" + environment_name + "][] type='checkbox' value=" + val.id + "><label for=" + val.id + ">" + val.hostname + "</label>";
      // otherwise just make a standard input
      } else {
        my_cool_input = "i was not checked... :(";
        var $input = "<input class='server_checkbox' id=" + val.id + " name=servers[" + environment_name +"][] type='checkbox' value=" + val.id + "><label for=" + val.id + ">" + val.hostname + "</label>";
      }

      alert(my_cool_input);  // will print something guaranteed
      alert(input); // will be undefined, because there is no input within scope