The final widget looks like:

Finished version of the CanJS File Navigator Guide (Advanced) on jsbin.com Open in JSFiddle

Note: If you don’t see any files show up, run the JS Bin again. This JS Bin uses randomly generated files, so it’s possible nothing shows up.

Start this tutorial by cloning the following JS Bin:

Starter version of the CanJS File Navigator Guide (Advanced) on jsbin.com Open in JSFiddle

This JS Bin has initial prototype HTML and CSS which is useful for getting the application to look right.

The following sections are broken down into:

• Problem - A description of what the section is trying to accomplish.
• Things to know - Information about CanJS that is useful for solving the problem.
• Solution - The solution to the problem.

Watch a video of us building this recipe here:

Build a service layer with fixtures

Problem

Make an /api/entities service layer that provides the files and folders for another folder. An entity can be either a file or folder. A single entity looks like:

{
  id: "2",
  name: "dogs",
  parentId: "0",     // The id of the folder this file or folder is within.
  type: "folder",    // or "file",
  hasChildren: true  // false for a folder with no children, or a file
}

To get the list of files and folders within a given folder, a GET request should be made as follows:

GET /api/entities?folderId=0

This should return the list of folders and files directly within that folder like:

{
  data: [
   { id: "7", name: "pekingese.png", parentId: "0", type: "file",   hasChildren: false },
   { id: "8", name: "poodles",       parentId: "0", type: "folder", hasChildren: false },
   { id: "9", name: "hounds",        parentId: "0", type: "folder", hasChildren: true }
  ]
}

The first level files and folders should have a parentId of "0".

Things to know

• can-fixture is used to trap AJAX requests like:

  can.fixture("/api/entities", function(request) {
    // request.data.folderId -> "1"
    return {data: [ ... ]}
  })
  

• store can be used to automatically filter records using the query string:

  var entities = [ ... ];
  var entitiesStore = can.fixture.store( entities );
  can.fixture("/api/entities", entitiesStore);
  

• rand can be used to create a random integer:

  can.fixture.rand(10) //-> 10
  can.fixture.rand(10) //-> 0
  

Solution

First, let’s make a function that generates an array of entities that will be stored on our fake server. Update the JavaScript tab to:

// Stores the next entity id to use.
var entityId = 1;

// Returns an array of entities for the given `parentId`.
// Makes sure the `depth` of entities doesn’t exceed 5.
var makeEntities = function(parentId, depth) {
  if (depth > 5) {
    return [];
  }
  // The number of entities to create.
  var entitiesCount = can.fixture.rand(10);

  // The array of entities we will return.
  var entities = [];

  for (var i = 0; i < entitiesCount; i++) {

    // The id for this entity
    var id = "" + (entityId++);

    // If the entity is a folder or file
    var isFolder = Math.random() > 0.3;

    // The children for this folder.
    var children = isFolder ? makeEntities(id, depth+1) : [];

    var entity = {
      id: id,
      name: (isFolder ? "Folder" : "File") + " " + id,
      parentId: parentId,
      type: (isFolder ? "folder" : "file"),
      hasChildren: children.length > 0
    };
    entities.push(entity);

    // Add the children of a folder
    [].push.apply(entities,  children)

  }
  return entities;
};

Next, let’s make those entities, create a store to house them, and trap AJAX requests to use that store:

// Stores the next entity id to use.
var entityId = 1;

// Returns an array of entities for the given `parentId`.
// Makes sure the `depth` of entities doesn’t exceed 5.
var makeEntities = function(parentId, depth) {
  if (depth > 5) {
    return [];
  }
  // The number of entities to create.
  var entitiesCount = can.fixture.rand(10);

  // The array of entities we will return.
  var entities = [];

  for (var i = 0; i < entitiesCount; i++) {

    // The id for this entity
    var id = "" + (entityId++);

    // If the entity is a folder or file
    var isFolder = Math.random() > 0.3;

    // The children for this folder.
    var children = isFolder ? makeEntities(id, depth+1) : [];

    var entity = {
      id: id,
      name: (isFolder ? "Folder" : "File") + " " + id,
      parentId: parentId,
      type: (isFolder ? "folder" : "file"),
      hasChildren: children.length > 0
    };
    entities.push(entity);

    // Add the children of a folder
    [].push.apply(entities,  children)

  }
  return entities;
};

// Make the entities for the demo
var entities = makeEntities("0", 0);

// Add them to a client-like DB store
var entitiesStore = can.fixture.store(entities);

// Trap requests to /api/entities to read items from the entities store.
can.fixture("/api/entities", entitiesStore);

// Make requests to /api/entities take 1 second
can.fixture.delay = 1000;

Create the Entity Model

The problem

When we load entities from the server, it’s useful to convert them into Entity type instances. We will want to create an observable Entity type using can-define/map/map so we can do:

var entity = new Entity({
  id: "2",
  name: "dogs",
  parentId: "0",     // The id of the folder this file or folder is within.
  type: "folder",    // or "file",
  hasChildren: true  // false for a folder with no children, or a file
});

entity.on("name", function(ev, newName) {
  console.log("entity name changed to ", newName);
});

entity.name = "cats" //-> logs "entity name changed to cats"

Things to know

You can create a DefineMap type using DefineMap.extend with the type’s properties and the properties’ types like:

Type = can.DefineMap.extend({
  id: "string",
  hasChildren: "boolean",
  ...
});

The solution

Extend can.DefineMap with each property and its type as follows:

// Stores the next entity id to use.
var entityId = 1;

// Returns an array of entities for the given `parentId`.
// Makes sure the `depth` of entities doesn’t exceed 5.
var makeEntities = function(parentId, depth) {
  if (depth > 5) {
    return [];
  }
  // The number of entities to create.
  var entitiesCount = can.fixture.rand(10);

  // The array of entities we will return.
  var entities = [];

  for (var i = 0; i < entitiesCount; i++) {

    // The id for this entity
    var id = "" + (entityId++);

    // If the entity is a folder or file
    var isFolder = Math.random() > 0.3;

    // The children for this folder.
    var children = isFolder ? makeEntities(id, depth+1) : [];

    var entity = {
      id: id,
      name: (isFolder ? "Folder" : "File") + " " + id,
      parentId: parentId,
      type: (isFolder ? "folder" : "file"),
      hasChildren: children.length > 0
    };
    entities.push(entity);

    // Add the children of a folder
    [].push.apply(entities,  children)

  }
  return entities;
};

// Make the entities for the demo
var entities = makeEntities("0", 0);

// Add them to a client-like DB store
var entitiesStore = can.fixture.store(entities);

// Trap requests to /api/entities to read items from the entities store.
can.fixture("/api/entities", entitiesStore);

// Make requests to /api/entities take 1 second
can.fixture.delay = 1000;

var Entity = can.DefineMap.extend({
  id: "string",
  name: "string",
  parentId: "string",
  hasChildren: "boolean",
  type: "string"
});

Connect the Entity model to the service layer

The problem

We want to be able to load a list of Entity instances from GET /api/entities with:

Entity.getList({parentId: "0"}).then(function(entities) {
    console.log(entities.get()) //-> [ Entity{id: "1", parentId: "0", ...}, ...]
});

Things to know

can.connect.baseMap() can connect a Map type to a url like:

can.connect.baseMap({
  Map: Entity,
  url: "URL"
});

The solution

Use can.connect.baseMap to connect Entity to /api/entities like:

// Stores the next entity id to use.
var entityId = 1;

// Returns an array of entities for the given `parentId`.
// Makes sure the `depth` of entities doesn’t exceed 5.
var makeEntities = function(parentId, depth) {
  if (depth > 5) {
    return [];
  }
  // The number of entities to create.
  var entitiesCount = can.fixture.rand(10);

  // The array of entities we will return.
  var entities = [];

  for (var i = 0; i < entitiesCount; i++) {

    // The id for this entity
    var id = "" + (entityId++);

    // If the entity is a folder or file
    var isFolder = Math.random() > 0.3;

    // The children for this folder.
    var children = isFolder ? makeEntities(id, depth+1) : [];

    var entity = {
      id: id,
      name: (isFolder ? "Folder" : "File") + " " + id,
      parentId: parentId,
      type: (isFolder ? "folder" : "file"),
      hasChildren: children.length > 0
    };
    entities.push(entity);

    // Add the children of a folder
    [].push.apply(entities,  children)

  }
  return entities;
};

// Make the entities for the demo
var entities = makeEntities("0", 0);

// Add them to a client-like DB store
var entitiesStore = can.fixture.store(entities);

// Trap requests to /api/entities to read items from the entities store.
can.fixture("/api/entities", entitiesStore);

// Make requests to /api/entities take 1 second
can.fixture.delay = 1000;

var Entity = can.DefineMap.extend({
  id: "string",
  name: "string",
  parentId: "string",
  hasChildren: "boolean",
  type: "string"
});

can.connect.baseMap({
  Map: Entity,
  url: "/api/entities"
});

Create the ROOT entity and render it

The problem

We need to begin converting the static HTML the designer gave us into live HTML. This means rendering it in a template. We’ll start slow by rendering the root parent folder’s name in the same way it’s expected by the designer.

Things to know

• CanJS uses can-stache to render data in a template and keep it live. Templates can be authored in <script> tags like:

  <script type="text/stache" id="app-template">
    TEMPLATE CONTENT
  </script>
  

  A can-stache template uses {{key}} magic tags to insert data into the HTML output like:

  <script type="text/stache" id="app-template">
    {{something.name}}
  </script>
  

• Load a template from a <script> tag with can.stache.from like:

  var template = can.stache.from(SCRIPT_ID);
  

• Render the template with data into a documentFragment like:

  var frag = template({
    something: {name: "Derek Brunson"}
  });
  

• Insert a fragment into the page with:

  document.body.appendChild(frag);
  

• You can create an Entity instance as follows:

  var folder = new Entity({...});
  

  Where {...} is an object of the properties you need to create like {id: "0", name: "ROOT", ...}. Pass this to the template.

The solution

Update the HTML tab to render the folder’s name.

<script type="text/stache" id="app-template">
  <span>{{folder.name}}</span>
</script>

Update the JavaScript tab to:

1. Create a folder Entity instance.
2. Load the app-template. Renders it with folder instance, and inserts the result in the <body> element.

// Stores the next entity id to use.
var entityId = 1;

// Returns an array of entities for the given `parentId`.
// Makes sure the `depth` of entities doesn’t exceed 5.
var makeEntities = function(parentId, depth) {
  if (depth > 5) {
    return [];
  }
  // The number of entities to create.
  var entitiesCount = can.fixture.rand(10);

  // The array of entities we will return.
  var entities = [];

  for (var i = 0; i < entitiesCount; i++) {

    // The id for this entity
    var id = "" + (entityId++);

    // If the entity is a folder or file
    var isFolder = Math.random() > 0.3;

    // The children for this folder.
    var children = isFolder ? makeEntities(id, depth+1) : [];

    var entity = {
      id: id,
      name: (isFolder ? "Folder" : "File") + " " + id,
      parentId: parentId,
      type: (isFolder ? "folder" : "file"),
      hasChildren: children.length > 0
    };
    entities.push(entity);

    // Add the children of a folder
    [].push.apply(entities,  children)

  }
  return entities;
};

// Make the entities for the demo
var entities = makeEntities("0", 0);

// Add them to a client-like DB store
var entitiesStore = can.fixture.store(entities);

// Trap requests to /api/entities to read items from the entities store.
can.fixture("/api/entities", entitiesStore);

// Make requests to /api/entities take 1 second
can.fixture.delay = 1000;

var Entity = can.DefineMap.extend({
  id: "string",
  name: "string",
  parentId: "string",
  hasChildren: "boolean",
  type: "string"
});

can.connect.baseMap({
  Map: Entity,
  url: "/api/entities"
});

var folder = new Entity({
  id: "0",
  name: "ROOT/",
  hasChildren: true,
  type: "folder"
});

var template = can.stache.from("app-template");
var frag = template({
  folder: folder
});

document.body.appendChild( frag );

Render the ROOT entities children

The problem

In this section, we’ll list the files and folders within the root folder.

Things to know

• Use {{#if(value)}} to do if/else branching in can-stache.
• Use {{#each(value)}} to do looping in can-stache.
• Use {{#eq(value1, value2)}} to test equality in can-stache.
• Promises are observable in can-stache. Given a promise somePromise, you can:
  • Check if the promise is loading like: {{#if(somePromise.isPending)}}.
  • Loop through the resolved value of the promise like: {{#each(somePromise.value)}}.
• Write <div class="loading">Loading</div> when files are loading.
• Write a <ul> to contain all the files. Within the <ul> there should be:
  • An <li> with a class attribute that includes file or folder and hasChildren if the folder has children.
  • The <li> should have 📝 <span>{{FILE_NAME}}</span> if a file and 📁 <span>{{FOLDER_NAME}}</span> if a folder.

The solution

The following uses entitiesPromise to write <div class="loading">Loading</div> while the promise is pending, and then writes out an <li> for each entity in the resolved entitiesPromise:

<script type="text/stache" id="app-template">
  <span>{{folder.name}}</span>
  {{#if(entitiesPromise.isPending)}}
    <div class="loading">Loading</div>
  {{else}}
    <ul>
      {{#each(entitiesPromise.value)}}
        <li class="{{type}} {{#if(hasChildren)}}hasChildren{{/if}}">
          {{#eq(type, 'file')}}
            📝 <span>{{name}}</span>
          {{else}}
            📁 <span>{{name}}</span>
          {{/eq}}
        </li>
      {{/each}}
    </ul>
  {{/if}}
</script>

The following adds an entitiesPromise to data passed to the template. entitiesPromise will contain the files and folders that are directly within the root folder.

// Stores the next entity id to use.
var entityId = 1;

// Returns an array of entities for the given `parentId`.
// Makes sure the `depth` of entities doesn’t exceed 5.
var makeEntities = function(parentId, depth) {
  if (depth > 5) {
    return [];
  }
  // The number of entities to create.
  var entitiesCount = can.fixture.rand(10);

  // The array of entities we will return.
  var entities = [];

  for (var i = 0; i < entitiesCount; i++) {

    // The id for this entity
    var id = "" + (entityId++);

    // If the entity is a folder or file
    var isFolder = Math.random() > 0.3;

    // The children for this folder.
    var children = isFolder ? makeEntities(id, depth+1) : [];

    var entity = {
      id: id,
      name: (isFolder ? "Folder" : "File") + " " + id,
      parentId: parentId,
      type: (isFolder ? "folder" : "file"),
      hasChildren: children.length > 0
    };
    entities.push(entity);

    // Add the children of a folder
    [].push.apply(entities,  children)

  }
  return entities;
};

// Make the entities for the demo
var entities = makeEntities("0", 0);

// Add them to a client-like DB store
var entitiesStore = can.fixture.store(entities);

// Trap requests to /api/entities to read items from the entities store.
can.fixture("/api/entities", entitiesStore);

// Make requests to /api/entities take 1 second
can.fixture.delay = 1000;

var Entity = can.DefineMap.extend({
  id: "string",
  name: "string",
  parentId: "string",
  hasChildren: "boolean",
  type: "string"
});

can.connect.baseMap({
  Map: Entity,
  url: "/api/entities"
});

var folder = new Entity({
  id: "0",
  name: "ROOT/",
  hasChildren: true,
  type: "folder"
});

var template = can.stache.from("app-template");
var frag = template({
  entitiesPromise: Entity.getList({parentId: "0"}),
  folder: folder
});

document.body.appendChild( frag );

Toggle children with a ViewModel

The problem

We want to hide the root folder’s children until the root folder is clicked on. An subsequent clicks on the root folder’s name should toggle if the children are displayed.

Things to know

• CanJS uses [guides/technicalViewModels#MaintainableMVVM ViewModels] to manage the behavior of views. ViewModels can have their own state, such as if a folder isOpen and should be showing its children. ViewModels are constructor functions created with can.DefineMap.

• can.DefineMap can detail the type of a property with another type like:

  var Address = can.DefineMap.extend({
    street: "string",
    city: "string"
  });
  var Person = can.DefineMap.extend({
    address: Address
  });
  

• can.DefineMap can also specify default values:

  var Person = can.DefineMap.extend({
    address: Address,
    age: {value: 33}
  });
  

• can.DefineMap can also specify a default value and a type:

  var Person = can.DefineMap.extend({
    address: Address,
    age: {value: 33, type: "number"}
  });
  

• can.DefineMap can also have methods:

  var Person = can.DefineMap.extend({
    address: Address,
    age: {value: 33, type: "number"},
    birthday: function() {
      this.age++;
    }
  });
  

• Use on:event to listen to an event on an element and call a method in can-stache. For example, the following calls doSomething() when the <div> is clicked.

  <div on:click="doSomething()"> ... </div>
  

The solution

The following:

• Defines a FolderVM type that will manage the UI state around a folder. Specifically FolderVM has:
  • folder which references the folder being displayed.
  • entitiesPromise which will be a promise of all files for that folder.
  • isOpen which tracks if the folder’s children should be displayed.
  • toggleOpen which changes isOpen.
• Creates an instance of the FolderVM and uses it to render the template.

// Stores the next entity id to use.
var entityId = 1;

// Returns an array of entities for the given `parentId`.
// Makes sure the `depth` of entities doesn’t exceed 5.
var makeEntities = function(parentId, depth) {
  if (depth > 5) {
    return [];
  }
  // The number of entities to create.
  var entitiesCount = can.fixture.rand(10);

  // The array of entities we will return.
  var entities = [];

  for (var i = 0; i < entitiesCount; i++) {

    // The id for this entity
    var id = "" + (entityId++);

    // If the entity is a folder or file
    var isFolder = Math.random() > 0.3;

    // The children for this folder.
    var children = isFolder ? makeEntities(id, depth+1) : [];

    var entity = {
      id: id,
      name: (isFolder ? "Folder" : "File") + " " + id,
      parentId: parentId,
      type: (isFolder ? "folder" : "file"),
      hasChildren: children.length > 0
    };
    entities.push(entity);

    // Add the children of a folder
    [].push.apply(entities,  children)

  }
  return entities;
};

// Make the entities for the demo
var entities = makeEntities("0", 0);

// Add them to a client-like DB store
var entitiesStore = can.fixture.store(entities);

// Trap requests to /api/entities to read items from the entities store.
can.fixture("/api/entities", entitiesStore);

// Make requests to /api/entities take 1 second
can.fixture.delay = 1000;

var Entity = can.DefineMap.extend({
  id: "string",
  name: "string",
  parentId: "string",
  hasChildren: "boolean",
  type: "string"
});

can.connect.baseMap({
  Map: Entity,
  url: "/api/entities"
});

var folder = new Entity({
  id: "0",
  name: "ROOT/",
  hasChildren: true,
  type: "folder"
});

var FolderVM = can.DefineMap.extend({
  folder: Entity,
  entitiesPromise: {
    value: function() {
      return Entity.getList({parentId: this.folder.id});
    }
  },
  isOpen: {type: "boolean", value: false},
  toggleOpen: function() {
    this.isOpen = !this.isOpen;
  }
});

// Create an instance of `FolderVM` with the root folder
var rootFolderVM = new FolderVM({
  folder: folder
});

var template = can.stache.from("app-template");
var frag = template(rootFolderVM);

document.body.appendChild( frag );

The following wraps the listing of child entities with a {{#if(isOpen)}} {{/if}}:

<script type="text/stache" id="app-template">
  <span on:click="toggleOpen()">{{folder.name}}</span>
  {{#if(isOpen)}}
  {{#if(entitiesPromise.isPending)}}
    <div class="loading">Loading</div>
  {{else}}
    <ul>
      {{#each(entitiesPromise.value)}}
        <li class="{{type}} {{#if(hasChildren)}}hasChildren{{/if}}">
          {{#eq(type, 'file')}}
            📝 <span>{{name}}</span>
          {{else}}
            📁 <span>{{name}}</span>
          {{/eq}}
        </li>
      {{/each}}
    </ul>
  {{/if}}
  {{/if}}
</script>

Create an <a-folder> custom element to manage folder behavior

The problem

Now we want to make all the folders able to open and close. This means creating a FolderVM for every folder entity.

Things to know

• can.Component is used to create custom elements like:

  var MyComponentVM = DefineMap.extend({
    message: {value: "Hello There!"}
  });
  
  can.Component.extend({
    tag: "my-component",
    ViewModel: MyComponentVM,
    view: can.stache("<h1>{{message}}</h1>");
  });
  

  This component will be created anytime a <my-component> element is found in the page. When the component is created, it creates an instance of it’s ViewModel, in this case MyComponentVM.

• You can pass data to a component’s ViewModel with {data-bindings} like:

  <my-component message:from="'Hi There'" />
  

  This sets message on the ViewModel to 'Hi There'. You can also send data within stache like:

  <my-component message:from="greeting" />
  

  This sets message on the ViewModel to what greeting is in the stache template.

• A component’s [View] is rendered inside the component. This means that if the following is in a template:

  <my-component {message}="'Hi There'" />
  

  The following will be inserted into the page:

  <my-component {message}="'Hi There'"><h1>Hi There</h1></my-component>
  

• this in a stache template refers to the current context of a template or section.

  For example, the this in this.name refers to the context object:

  var template = stache("{{this.name}}");
  var context = {name: "Justin"};
  template(context);
  

  Or, when looping through a list of items, this refers to each item:

  {{#each(items)}}
    <li>{{this.name}}</li> <!-- this is each item in items -->
  {{/each}}
  

The solution

The following:

1. Changes the app-template to use the <a-folder> component to render the root folder. It passes the root folder as folder to the <a-folder> component’s ViewModel. It also sets the <a-folder> component’s ViewModel’s isOpen property to true.
2. Moves the content that was in app-template to the folder-template <script> tag.
3. Recursively renders each child folder with <a-folder {folder}="this" />.

<script type="text/stache" id="app-template">
  <a-folder folder:from="this" isOpen:from="true" />        <!-- CHANGED -->
</script>

<!-- CONTENT FROM app-template-->
<script type="text/stache" id="folder-template">
  <span on:click="toggleOpen()">{{folder.name}}</span>
  {{#if(isOpen)}}
  {{#if(entitiesPromise.isPending)}}
    <div class="loading">Loading</div>
  {{else}}
    <ul>
      {{#each(entitiesPromise.value)}}
        <li class="{{type}} {{#if(hasChildren)}}hasChildren{{/if}}">
          {{#eq(type, 'file')}}
            📝 <span>{{name}}</span>
          {{else}}
            📁 <a-folder folder:from="this" />            <!-- CHANGED -->
          {{/eq}}
        </li>
      {{/each}}
    </ul>
  {{/if}}
  {{/if}}
</script>

The following:

1. Defines a custom <a-folder> element that manages its behavior with FolderVM and uses it to render a folder-template template.
2. Renders the app-template with the root parent folder instead of the rootFolderVM.

// Stores the next entity id to use.
var entityId = 1;

// Returns an array of entities for the given `parentId`.
// Makes sure the `depth` of entities doesn’t exceed 5.
var makeEntities = function(parentId, depth) {
  if (depth > 5) {
    return [];
  }
  // The number of entities to create.
  var entitiesCount = can.fixture.rand(10);

  // The array of entities we will return.
  var entities = [];

  for (var i = 0; i < entitiesCount; i++) {

    // The id for this entity
    var id = "" + (entityId++);

    // If the entity is a folder or file
    var isFolder = Math.random() > 0.3;

    // The children for this folder.
    var children = isFolder ? makeEntities(id, depth+1) : [];

    var entity = {
      id: id,
      name: (isFolder ? "Folder" : "File") + " " + id,
      parentId: parentId,
      type: (isFolder ? "folder" : "file"),
      hasChildren: children.length > 0
    };
    entities.push(entity);

    // Add the children of a folder
    [].push.apply(entities,  children)

  }
  return entities;
};

// Make the entities for the demo
var entities = makeEntities("0", 0);

// Add them to a client-like DB store
var entitiesStore = can.fixture.store(entities);

// Trap requests to /api/entities to read items from the entities store.
can.fixture("/api/entities", entitiesStore);

// Make requests to /api/entities take 1 second
can.fixture.delay = 1000;

var Entity = can.DefineMap.extend({
  id: "string",
  name: "string",
  parentId: "string",
  hasChildren: "boolean",
  type: "string"
});

can.connect.baseMap({
  Map: Entity,
  url: "/api/entities"
});

var folder = new Entity({
  id: "0",
  name: "ROOT/",
  hasChildren: true,
  type: "folder"
});

var FolderVM = can.DefineMap.extend({
  folder: Entity,
  entitiesPromise: {
    value: function() {
      return Entity.getList({parentId: this.folder.id});
    }
  },
  isOpen: {type: "boolean", value: false},
  toggleOpen: function() {
    this.isOpen = !this.isOpen;
  }
});

can.Component.extend({
  tag: "a-folder",
  ViewModel: FolderVM,
  view: can.stache.from("folder-template")
});

var template = can.stache.from("app-template");
var frag = template(folder);

document.body.appendChild( frag );

Result

When complete, you should have a working file-navigation widget like the following JS Bin:

Finished version of the CanJS File Navigator Guide (Advanced) on jsbin.com Open in JSFiddle