Polymer Code Lab at Dev Fest Prague 2014
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Notes Application Polymer Code Lab Prague 2014

The goal of this code lab is to create note-taking application in Polymer. We create simple application which can add notes, delete selected note or all notes in the list and we also try local storage to save the notes into the browser.

You will learn:

  • how to write applications and Polymer
  • how to use Polymer Core and Paper elements
  • how to write your own Polymer elements
  • how to integrate Polymer elements into your application

Download the prepared project from Github and open it in Chrome Dev Editor. We prepared everything important for you so you don't have to solve any CSS styling and HTML structure, and you can directly explore how to write Dart application.

Project is divided into steps according to this Code Lab. Try to run the application from step06/ and see how it works.

Notes application

Step 1 - Empty project

Start in step01/ folder. This is a default Polymer project with HTML template and styles and only shows simple page with Polymer elements.

We update this code, add more functionality and at the end we will have nice notes application.

Step 2 - Create new Polymer element + using Paper + Core elements

In this step we create our own element and we learn, how to use Polymer Paper and Core elements in our application.

First create prague-notes.html file.

Then you need to remove all imports and change it to our element in index.html file to:

	<!-- import notes element -->
	<link rel="import" href="prague-notes.html">

And use our element in HTML body:


The whole index.html file looks like this:

<!doctype html>

  <title>Note app</title>

  <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0">
  <meta name="mobile-web-app-capable" content="yes">
  <meta name="apple-mobile-web-app-capable" content="yes">

  <script src="../bower_components/webcomponentsjs/webcomponents.js"></script>

  <!-- import notes element -->
  <link rel="import" href="prague-notes.html">

<body unresolved>

In file prague-notes.html we need to make several changes. At first, we need to add element definition. Add <polymer-element> tag to prague-notes.html with <template> and <script> tags inside. The element name should be same as the name of file.

<polymer-element name="prague-notes">

Add some CSS styles inside <template element:

    #notes-delete-all {
      background: red;
    core-toolbar h2 {
      color: white;
    core-toolbar paper-input {
      width: 100%;

Now, we can start adding Polymer Core and Paper elements to our element. First, we need to import elements, which we want to use. We will use paper input, paper button, core toolbar and core icon elements.

At the beggining of the file, we need to add the following import statements:

<link rel="import" href="../bower_components/paper-input/paper-input.html">
<link rel="import" href="../bower_components/paper-button/paper-button.html">
<link rel="import" href="../bower_components/core-icon/core-icon.html">
<link rel="import" href="../bower_components/core-toolbar/core-toolbar.html">

In our template body, we can now easily use these elements. We will have core-toolbar element with three sub-elements: title, input box for adding new note and button, which deletes all.

Last element in prague-notes will be list of all notes, but we will add this in step 3. For now, we will insert only empty <div> element.

HTML body of our element will be the following:

      <h2>Notes app</h2>

      <span flex>
        <paper-input floatinglabel label="Enter note" id="newNoteInput"></paper-input>

      <paper-button raised id="notes-delete-all">
        <core-icon icon="clear">
        Delete all

    <div class="content">


Last thing, that is missing is JavaScript code for our element. Content of the <script> tag will be following:

  <script type="text/javascript">

We can also delete unused files main.js and styles.css.

You should be able to run the project now. If you select index.html file and click on the play button run. You should see our appplication with toolbar.

Step 3 - Create new Polymer element and bind model with template

In this step we create another element prague-note, which will be single item in our list of notes. And we will use this element as a template for list of our notes.

At first, we create new element in file prague-note.html. We will use the following paper elements: paper button, papaer icon button, paper shadow and paper ripple.

Add these imports into our newly created file prague-note.html:

<link rel="import" href="../bower_components/polymer/polymer.html">
<link rel="import" href="../bower_components/paper-button/paper-button.html">
<link rel="import" href="../bower_components/paper-icon-button/paper-icon-button.html">
<link rel="import" href="../bower_components/paper-shadow/paper-shadow.html">
<link rel="import" href="../bower_components/paper-ripple/paper-ripple.html">

We add element declaration with <script> tag:

<polymer-element name="prague-note">
  <script type="text/javascript">

We add some css styles:

      .note {
        padding: 0.5em;
        margin: 0.5em;
      .note .note-text {
        margin: 0.5em;
        font-size: 2em;
      paper-icon-button.delete {
        color: red;
        float: right;
        padding-top: 3ex;

And finally we can add Paper elements. We start with <paper-shadow> element, which will have horizontal layout:

    <paper-shadow class="note" layout horizontal z="2">


Inside this element we can add <div> element with our note's text and with nice ripple effect. Next we add delete icon button.

    <paper-shadow class="note" layout horizontal z="2">
      <paper-ripple fit></paper-ripple>
      <div flex class="note-text">
        <paper-icon-button icon="clear" class="delete"></paper-icon-button>

Now we need to add note attribute to our element. We need to update our element definition:

<polymer-element name="prague-note" attributes="note">

And we also need to add JavaScript for this attribute to bind it with our note variable via property publish.

  <script type="text/javascript">
      publish: {
        note: ''

Now we can use our new element prague-note in our html. We want to use this element for each item in notes list. So we can easily use polymer template tag with repeat attribute. In prague-notes.html you need to import our element:

<link rel="import" href="prague-note.html">

Add inside content <div> in prague-notes.html we can use our element:

      <template repeat="{{note in notes}}">
        <prague-note note="{{note}}"></prague-note>

For every note object in notes array we render prague-note element, with note attribute, which sets the note object into our note property in prague-notes element.

In prague-notes.html file, we need to declare our notes collection and we can add some data. When we add property to Polymer object, that property is automatically available in our template and every change will be propragated to template.

  <script type="text/javascript">
      notes: ['Learn Polymer', 'Build Polymer App']

Step 4 - Adding new notes

In this step we add a method, that will add a new note to our list of notes.

In prague-notes.html file we add on-change and value attribute to paper-input element and , which will call createNote method and set newNote varaible in our JavaScript.

        <paper-input floatinglabel label="Enter note" id="newNoteInput" on-change="{{createNote}}" value="{{newNote}}"></paper-input>

And in our JavaScript we set notes variable toempty array add new method createNote. This method uses newNote variable, which we declared in our template. When this method is run, we check if the value of input is not empaty and add data from our input to the list of our notes.

      notes: [],
      createNote: function() {
        if (this.newNote !== '') {
          this.newNote = '';

When you run your application, you should be able to add new notes to our list.

Step 5 - Deleting notes

In this step we add two methods. First method deletes single note from our list and second method deletes all the notes.

We will start with Delete all button. We need to add on-click attribute to our delete button in prague-notes.html file:

      <paper-button raised id="notes-delete-all" on-click="{{deleteAll}}">...</paper-button>

And our JavaScript we define new method deleteAll, which removes all data from our notes collection:

      deleteAll: function() {
        this.notes = [];

Now we need to add delete method for signle note. Before we start with this method, we need to add indexes to our notes in list, because we need to know, which note we want to delete.

We add indexes to our notes collection in template file prague-notes.html. We change our code to:

      <template repeat="{{note, i in notes}}">
        <prague-note note="{{note}}" index="{{i}}"></prague-note>

We also need to add this new index attribute to our prague-note element.

First add index to our attributes list in prague-note element definition:

<polymer-element name="prague-note" attributes="note index">

And we also need to add our index variable to publish property.

      publish: {
        note: '',
        index: 0

Now we can add on-click attribute to paper-icon-button element in prague-note to call new method deleteNote:

        <paper-icon-button icon="clear" class="delete" on-click="{{deleteNote}}"></paper-icon-button>

And we declare this method. Because the list of our notes is in parent element, we need to fire our custom event with name delete-note and with index of deleted note.

      deleteNote: function() {
        this.fire('delete-note', {'index': this.index});

Now we need to catch this event. We can declare that our element prague-notes should listen for these events and when this event is fired, we can call our method in prague-notes element. We can use on-delete-note attribute in element definition. The syntax for this attribute is on- and name of event. When we catch any event, we can call our custom method from that element. We need to change our prague-notes element declaration:

<polymer-element name="prague-notes" on-delete-note="{{deleteNote}}">

And we add new method deleteNote to prague-notes.html file. We get the index of note, which should be deleted and we can easily remove note on that index from our collection.

      deleteNote: function(event, note) {
        var index = note.index;
        this.notes.splice(index, 1);

Step 6 - Saving to local storage

We can improve our application to save all data to brower local storage, so when user closes or refreshes browser, tha data are still saved in browser. And if user opens the browser again he doesn't loose the data.

We can easily use core localstorage element. We need to include it in prague-notes.html file:

<link rel="import" href="../bower_components/core-localstorage/core-localstorage.html">

And now we can use the element and bind it to our notes variable. Now every time the notes varaible is changed, it's saved into local storage and when user reload the browser this element gets our notes from local storage and populate the notes varaible.

<core-localstorage id="storage" name="codelab-app-storage" value="{{notes}}"></core-localstorage>

Now when you refresh your browser, you should see all your notes, that were previously saved in your browser.