未捕获的ReferenceError：方法未定义。”-JSON，Ajax，JS

Question

我不断收到错误消息“未捕获的ReferenceError：未定义dropdown_fitness_json。”我认为，如果它不在ready函数之外，那么它将可以访问。

我已经验证我正在访问json数据，但是我一直在出错。我有没有得到的东西，还是只是我没有注意到的语法错误？ TIA！

HTML：

<div class="asynchronous_option">
                        <select id="plan_name" onchange = "dropdown_fitness_json()">
                            <option value="0">View Plan By Name</option>
                        </select>
                        </div><br>

<div id="plan_search_results">In results</div>

JS：

// ASYNCHRONOUS FITNESS PLAN 
    function dropdown_fitness_json() 
    {
        var fitness_plan_file = "./../json/fitness_plans.json";
        //get data back request
        var http_request = new XMLHttpRequest();

        try 
        {
            // Opera 8.0+, Firefox, Chrome, Safari
            http_request = new XMLHttpRequest();
        } 
        catch (e) 
        {
            // IE Browsers
            try 
            {
                http_request = new ActiveXObject("Msxml2.XMLHTTP");
            } 
            catch (e) 
            {
                try 
                {
                    http_request = new ActiveXObject("Microsoft.XMLHTTP");
                } 
                catch (e) 
                {
                    // alert something went wrong
                    alert("Something is wrong with your browser. Please refresh your page and try again.");
                    return false;
                }
            }
        }

        // anon function
        http_request.onreadystatechange = function () 
        {
            if (http_request.readyState === 4) 
            {
                // JS function JSON.parse parses JSON data
                var jsonObj = JSON.parse(http_request.responseText);

                // jsonObj variable now contains the data structure
                var fitness_plans_names = "";
                var plan_search_results = "";

                for (var i = 0; i < jsonObj.fitness_plans.length; i++) 
                {
                    if (jsonObj.names[i].id === document.getElementById("plan_name").value 
                            && document.getElementById("plan_name").value !== 0) 
                    {
                        //fitness_plans_names = fitness_plans_names 
                          //      + jsonObj.fitness_plans[i].name + "<br>";

                        plan_search_results = plan_search_results + 
                            jsonObj.fitness_plans[i].name + "<br>" +
                            jsonObj.fitness_plans[i].price + "<br>" +
                            jsonObj.fitness_plans[i].meal_type + "<br>" +
                            jsonObj.fitness_plans[i].duration + "<br>" +
                            jsonObj.fitness_plans[i].desc + "<br>";

                        // display individual plan info
                        // document.getElementById("plan_name").innerHTML = fitness_plans_names;
                        document.getElementById("plan_search_results").innerHTML = plan_search_results;
                    }
                    //document.getElementById("").innerHTML = plan_search_results;
                }
            }
        };

    //get data from json file asynchronously to populate dropdown lists
    http_request.open("GET", fitness_plan_file, true);
    http_request.send();
    }
    // end return search result function