A simple todo app in javascript

Asked in Box onsite interview. With a node.js server on backend.

$().ready(function() {
   $('#add').on('click', addTask);
   $('#tasks').on('click', markComplete);
   // Alternative way
   // var tasksElement = document.getElementById('tasks');
   // tasksElement.addEventListener('click', markComplete);
   //document.getElementById('task-input').onkeydown = function(e){
   $('#task-input').on('keydown', function(e) {
       if(e && e.keyCode == 13){
            addTask();
       }
   });

   function renderTask(result) {
        var checkboxContainerId = 'check' + result.id;
        var taskTextId = 'tasktext-' + result.id;
        if (result.done == '1') {
            checkedState = ' checked ';
        } else {
            checkedState = '';
        }
        taskHtml = '
';
        taskHtml += '';
        taskHtml += '' + result.data + '
';
        $('#tasks').append(taskHtml);
   }

   function taskAdded(result) {
        renderTask(result);
        $('#task-input').val('');
   }

   function renderResults(results) {
        results.forEach(renderTask);
   }

   function addTask(e) {
       url = 'http://localhost:9898/todo/tasks/create';
       inputData = $('#task-input').val();

       if (!inputData) {
           return;
       }
       $.ajax({
           url: url,
           type: "POST",
           data: {data: inputData} ,
           success: taskAdded,
       });
    }

    function markComplete(e) {
        var done;
        if (e.target && e.target.matches("input.task-checkbox")) {
            var taskId = $(e.target).attr('task-id');
            if ($(e.target).is(":checked")) {
                done = "1";
            } else {
                done = "-1";
            }
            var editUrl = 'http://localhost:9898/todo/tasks/' + taskId + '/edit';
            $.ajax({
               url: editUrl,
               type: "POST",
               data: {done: done},
               success: function(result) {
               }
            });
        }
    }

    var getTasksUrl = 'http://localhost:9898/todo/tasks';
    $.ajax({
       url: getTasksUrl,
       type: "GET",
       success: renderResults,
    });
}
);