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Mark Nadal edited this page Dec 6, 2019 · 2 revisions

This is a beginner's guide to building your first todo app! It should take someone with no prior HTML or JS experience over a half hour to complete, or take less than 5 minutes for an advanced developer to jump through.

Our goal is to make it so you can build the app of your dreams! All apps use the same core concepts, so by learning how to create a todo app you'll also learn how to build parts of your dream app.

Plus, we'll need an app to keep track of our thoughts and plans along the way, so it is a double win! Our todo app should give us the ability to write down our thoughts in a note, view them, and clear them off.

First, we need an interface for our app! Here is the code and a live preview: (note - the app doesn't work yet).

::: {codepen: 'link', tab1: 'codemirror'} :::
::: {editor: 'main'} :::
::: {startblock: '1'} :::
<html>
  <body>
::: {endblock: '1'} :::
    <h1>Title</h1>
::: {startblock: '2'} :::

    <form>
      <input><button>Add</button>
    </form>
			
    <ul></ul>
::: {endblock: '2'} :::
::: {startblock: '3'} :::
  </body>
</html>
::: {endblock: '3'} :::

How does it work? Well,

  • First, we must wrap all of our code in open and closing html tags so that the computer knows it is a web page.
  • Stuff inside of the body tag are the main contents of the page.
  • h1 is a tag for declaring a title, others include h2, h3 and so on for different sizes.
  • A form is a way for us to get information from a user.
  • One way is through an input, which lets the user type data in - it doesn't need a closing tag.
  • The button can be pressed, causing some action (that we will code) to happen.
  • ul is an unordered list which we will display our thoughts inside of.

Challenge

Try changing the h1 text in the editor from "Title" to the name of our app, "Thoughts".

::: {nextstepcompare: 'start'} :::

::: {startblock: '4'} :::
::: {insertblock: '1'} :::
    <h1>Thoughts</h1>
::: {insertblock: '2'} :::
::: {endblock: '4'} :::
::: {insertblock: '3'} :::

::: {nextstepcompare: 'end'} :::

::: {step: 'Step 2'} :::

::: {codepen: 'link', tab1: 'codemirror'} :::
::: {editor: 'main'} :::
::: {insertblock: '4'} :::
<!-- Replace this Comment Line with the Code in the Step below! -->
::: {insertblock: '3'} :::

HTML controls the layout - so how do we then control what happens when a user presses the 'add' button? This is done with javascript!

Using javascript by itself can be verbose, so we will use a popular tool called jQuery to keep things simple. Other tools, like React or Vue, abstract things into a framework and should be learned after one understands the basics.

We also need a tool to store our data, so we will include GUN as well!

Insert the following as new lines between <ul></ul> and </body> in the editor, replacing the comment line:

    <script src="https://code.jquery.com/jquery-1.11.3.min.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/gun/gun.js"></script>
    <script>
      $("h1").text("Good job! You'll replace this line in the next step!");
    </script>

Here is what it is doing:

  • The script tag tells the browser to use some javascript code, and src is where to load it from.
  • Putting something inside of double "" or single '' quotations treats it as normal text, not code.
  • jQuery is a function, its name is $ which can be called with parenthesis ().
  • A function is just a fancy word for a reusable piece of code that does something when we call it.
  • Calling $ with "h1" as its input gives us a reference to the corresponding HTML tag.
  • We can use the . separator on the reference to access more functions.
  • Calling the text function tells the computer to dynamically change the text of our reference, the title.
  • A semicolon ; marks the end of a javascript sentence in the same way a period marks the end of a sentence.

This is why we call it code! We use a bunch of strange symbols to tell the computer to do things. Even the most advanced developers get things wrong all the time, but that is okay, you just keep trying!

::: {nextstepcompare: 'start'} :::

::: {startblock: '5'} :::
::: {insertblock: '4'} :::
    <script src="https://code.jquery.com/jquery-1.11.3.min.js"></script>
    <script src="https://cdn.jsdelivr.net/npm/gun/gun.js"></script>
    <script>
::: {endblock: '5'} :::
::: {startblock: '6'} :::
      $("h1").text("Good job! You'll replace this line in the next step!");
::: {endblock: '6'} :::
::: {startblock: '7'} :::
    </script>
::: {insertblock: '3'} :::
::: {endblock: '7'} :::

::: {nextstepcompare: 'end'} :::

::: {step: 'Step 3'} :::

::: {codepen: 'link', tab1: 'codemirror'} :::
::: {editor: 'main'} :::
::: {insertblock: '5'} :::
::: {insertblock: '6'} :::
::: {insertblock: '7'} :::

Now that we know something is working, we can actually start building our app. Let's replace the message line entirely with code that receives input from the user:

      $('form').on('submit', function(event){
        event.preventDefault();
        $("h1").text("We got your thought! " + $("input").val());
      });

What's going on here?

  • Calling jQuery's $ function with "form" instead of "h1" now gives us a reference to the HTML form tag.
  • Like the text function from the previous step, on is a function that can be accessed via the . separator.
  • on takes two inputs. First the text name of an event we want to react to, and then a function we create.
    • Events are predefined ways we can interact with a user, such as "mousemove" or a "keypress".
    • We use "submit" because it responds to both a button "click" and hitting your enter key on a form.
    • Our function will get called with the event every time the user does that action, allowing us to react to their input!
  • The default behavior of a form is to cause the browser to change pages which is annoying, so we prevent that by calling the preventDefault function on the event separated by the ..
  • Next up, we want to test if this works. So like before, we change the title by passing text to the $("h1").text() function.
  • Unlike other functions, $("input").val() gives us the actual value of the user's text, not a reference.
  • We can add this text to other text by using the + operator, that way our title will show what the user said.

Try it out!

::: {nextstepcompare: 'start'} :::

::: {insertblock: '5'} :::
::: {startblock: '8'} :::
      $('form').on('submit', function(event){
        event.preventDefault();
::: {endblock: '8'} :::
::: {startblock: '9'} :::
        $("h1").text("We got your thought! " + $("input").val());
::: {endblock: '9'} :::
::: {startblock: '10'} :::
      });
::: {endblock: '10'} :::
::: {insertblock: '7'} :::

::: {nextstepcompare: 'end'} :::

::: {step: 'Step 4'} :::

::: {codepen: 'link', tab1: 'codemirror'} :::
::: {editor: 'main'} :::
::: {insertblock: '5'} :::
/* Replace this Comment Line with the Code in the Step below! */
::: {insertblock: '8'} :::
::: {insertblock: '9'} :::
::: {insertblock: '10'} :::
::: {insertblock: '7'} :::

Now that users can jot down their thoughts, we need a place to save them. Let's start using GUN for just that.

var gun = Gun().get('thoughts');
  • The variable keyword tells javascript that we want to create a reference named gun that we can reuse.
  • We call Gun to start the database, which only needs to be done once per page load.
  • Now we want to open up a reference to some data, so we call get with the name of the data we want.
  • However, no data has been saved to thoughts yet! Let's fix that in the next step by using gun.

::: {nextstepcompare: 'start'} :::

::: {startblock: '11'} :::
::: {insertblock: '5'} :::
      var gun = Gun().get('thoughts');
::: {insertblock: '8'} :::
::: {endblock: '11'} :::
::: {insertblock: '9'} :::
::: {insertblock: '10'} :::
::: {insertblock: '7'} :::

::: {nextstepcompare: 'end'} :::

::: {step: 'Step 4'} :::

::: {codepen: 'link', tab1: 'codemirror'} :::
::: {editor: 'main'} :::
::: {insertblock: '11'} :::
::: {insertblock: '9'} :::
::: {insertblock: '10'} :::
::: {insertblock: '7'} :::

Replace the message line in the submit function with the following:

        gun.set($('input').val());
        $('input').val("");
  • We're telling gun to add the value of the input as an item in a set of thoughts.
  • Then we also want the input's value to become empty text, so we can add new thoughts later.

::: {nextstepcompare: 'start'} :::

::: {startblock: '12'} :::
::: {insertblock: '11'} :::
        gun.set($('input').val());
        $('input').val("");
::: {insertblock: '10'} :::
::: {endblock: '12'} :::
::: {insertblock: '7'} :::

::: {nextstepcompare: 'end'} :::

::: {step: 'Step 6'} :::

::: {codepen: 'link', tab1: 'codemirror'} :::
::: {editor: 'main'} :::
::: {insertblock: '12'} :::
/* Replace this Comment Line with the Code in the Step below! */
::: {insertblock: '7'} :::

Fantastic! Now that we can successfully store data, we want show the data! Replace the comment line in the editor with the following:

      gun.map().on(function(thought, id){
        var li = $('#' + id).get(0) || $('<li>').attr('id', id).appendTo('ul');
        if(thought){
          $(li).text(thought);
        } else {
          $(li).hide();
        }
      });
  • map tells gun to get each item in the set, one at a time, to do something with it.
  • What we do is the same as $'s on, which reacts to events. So does gun, it responds to any update on 'thoughts'.
  • We get the thought value itself and a unique identifier for the item in the set.
  • This next line looks scary, but read it like this, "make variable li equal to X or Y".
    • The X part asks $ to find the id in the HTML and get it.
    • In javascript, || means 'or', such that javascript will use X if it exist or it will use Y.
    • The Y part asks $ to create a new <li> HTML tag, set its id attribute to our id and append it to the end of the HTML ul list.
  • Finally, the javascript if statement either asks $ to make thought be the text of the li if thought exists, else hide the li from being displayed.
  • Altogether it says "Create or reuse the HTML list item and make sure it is in the HTML list, then update the text or hide the item if there is no text".

::: {nextstepcompare: 'start'} :::

::: {startblock: '13'} :::
::: {insertblock: '12'} :::
      gun.map().on(function(thought, id){
        var li = $('#' + id).get(0) || $('<li>').attr('id', id).appendTo('ul');
        if(thought){
          $(li).text(thought);
        } else {
          $(li).hide();
        }
      });
::: {endblock: '13'} :::
::: {insertblock: '7'} :::

::: {nextstepcompare: 'end'} :::

::: {step: 'Step 7'} :::

::: {codepen: 'link', tab1: 'codemirror'} :::
::: {editor: 'main'} :::
::: {insertblock: '13'} :::
/* Replace this Comment Line with the Code in the Step below! */
::: {insertblock: '7'} :::

Finally we want to be able to clear off our thoughts when we are done with them. The interface for this could be done in many different ways, but for simplicity we will use a double tap as the gesture to clear it off. Replace the comment line in the editor with this code.

      $('body').on('dblclick', 'li', function(event){
        gun.get(this.id).put(null);
      });
  • In order to react to any dblclick event rather than a specific one, we call on on the page's body as a whole.
  • But we want to filter the events to ones that happened only on any li tag. Fortunately, we can call on with an optional second input of li which does just that.
  • Inside a function we get a special this keyword in javascript, which $ uses as a reference to the original HTML tag that caused the event.
  • Calling get tells gun to filter its data to just the id of the thought we want to clear off.
  • Then calling put on that tells gun to update that thought to null, so we no longer have the thought.
  • And whenever an update happens, gun's on function from the previous step gets called again, which then hides the corresponding HTML list item.

::: {nextstepcompare: 'start'} :::

::: {startblock: '14'} :::
::: {insertblock: '13'} :::
      $('body').on('dblclick', 'li', function(event){
        gun.get(this.id).put(null);
      });
::: {insertblock: '7'} :::
::: {endblock: '14'} :::

::: {nextstepcompare: 'end'} :::

::: {step: 'Step 8'} :::

::: {codepen: 'link', tab1: 'codemirror'} :::
::: {editor: 'main'} :::
::: {insertblock: '14'} :::

Congratulations! You are all done, you have built your first GUN app!

In the next tutorial we will use GUN to synchronize data in realtime across multiple devices. We'll start by copying the app we made here and modifying it to become a chat app.

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