Early on in this Ramping Up tutorial, it was mentioned it would end with a little peak into JavaScript. If you are a total newbie when it comes to JavaScript, this last section might make less sense. However, still consider looking over it -- maybe you might find you like JavaScript, and could get curious to learn more. With JavaScript code, you can greatly expand what you can do with Modulo with custom functionality, create more interactive applications, games, better integrating APIs, process data, and more.

So far, our interactivity has been limited to binding state. In this final section, we will learn about connecting arbitrary events to methods, and also dipping our toes into the "full power" of JavaScript.


How many events are there? There are many, many events! We'll mostly just use click, but sometimes you'll need other events, such as when adding interactions for mouse motion, or adding in drag-and-drop. Read MDN's list of all events.

Now for perhaps the most important framework feature for interactive applications: Attaching arbitrary events. In Modulo, events are attached with the event directive, indicated by the @ sign.

The event directive

So far, we've learned how to use [state.bind] to add interactivity to a Component. Under the hood, [state.bind] attaches something called an "event listener". This is a bit of JavaScript code that waits for user interaction. The State CPart waits for the keyup event (e.g. when typing in an input) or the change event (e.g. when adjusting a slider). This is good enough for a lot of cases, but often we want to listen to other sorts of events. There are also events for clicking, mouse motion, scrolling, resizing, and so on. These are "activated" or "triggered" by the web browser when a user of your web site does one of these actions (types on the keyboard, moves the mouse, etc.). We'll need to use event directives to access these other events.

The most used event is the click event. Here's an example a click event:

<Template> <button @click:=state.items.reverse> Reverse the items! </button> </Template> <State items:='[ "a", "b", "c" ]' ></State>

Method? What methods are there? All "container" types of data have different "verbs" or "commands" you can do to it, which are called "methods". For example, just like you can reverse a line of people in real life by giving the command for everyone to turn around (so to speak), you can reverse an Array of people's names by giving the Array.reverse command. These enable different modifications to happen to the data contained within. By default, JavaScript comes with several very handy ones attached to the Array type, and we'll go over them all in this tutorial. However, for a full reference, you can refer to MDN's documentation: Array tutorial, Full list of Array methods

Let's break down the event directive in detail:

  • @click - all event directives start with @, so @click, @mouseover, @drag etc.
  • := - this is a data prop directive, which allows us to access state.items
  • state.items.reverse - this is accessing the items Array, and then on that, accessing the Array.reverse method, which will get activated when the click event happens

Just guessing, based on the text and the code you see here, what do you think this might do when a user clicks on the button? If you guessed it might "reverse" the state variable called "items", you would be correct!

Let's now try it out.

Try it now
  1. Examine the following code, and try the demo. What does clicking the button do?
<Template> <p>Items: {{ state.items|join }}</p> <button @click:=state.items.reverse >Reverse the items!</button> </Template> <State items:='[ "candy", "bread" ]' ></State>
  1. Examine the following code, and try the demo. What does each button do?
<Template> <p>Items: {{ state.items|join }}</p> <hr /> Remove last: <button @click:=state.items.pop>Array.pop</button> <hr /> Remove first: <button @click:=state.items.shift>Array.shift</button> </Template> <State items:='[ "zucchini", "oatmeal", "oranges", "apples", "candy", "bread" ]' ></State>
Comprehension Questions

Do you see how clicking on the buttons causes the Array to be reversed or removed or otherwise modified, and the component to rerender with the new look? Why do you think the component needs to "rerender"?

  • Answer: Modulo is based on a "change state & rerender" philosophy. That is, when you do an event, that should change the state, and then the component will automatically rerender, showing the new appearance based on the new values in the state. In this case, it's reversing the list.

Event payload

Many methods that we want to activate upon an event require extra information about the event to be useful. This extra data is added with a "payload=" attribute. For example, this button will activate the Array.fill method with a payload of `"X"``:

<button @click:=state.brands.fill payload="X" >Change to "X"</button>

This causes the "brands" Array to get each item replaced with the String "X". Payloads can also have data props, so you can use different values, e.g. if you wanted a number type, you'd write payload:=0

Let's practice events and payload by building up a shopping list app, which will use several Array methods, and many click events.

Try it now
  1. Examine the following example, that transforms our shopping list to something a bit less "balanced":
<Template> <p>Shopping list: {{ state.items|join }}</p> <hr /> <button @click:=state.items.fill payload="CANDY!!!!!!" >MAKE IT ALL CANDY!!</button> </Template> <State items:='[ "zucchini", "oatmeal", "oranges", "apples", "candy", "bread" ]' ></State>
  1. Now, examine this next app, which offers the user two options to "push" (add) onto a Array that starts empty:
<Template> <p>Shopping list: {{ state.items|join }}</p> <hr /> <button @click:=state.items.push payload="oatmeal" >Oatmeal</button> <button @click:=state.items.push payload="CANDY!!!" >Candy</button> </Template> <State items:=[] ></State>
  1. Examine the following code. It's more advanced. It has a list of different items, which it uses to generate the different buttons with different items:
<Template> <h3>Shopping list | {{ state.items|length }}</h3> <p>{{ state.items|join }}</p> <hr /> {% for favorite in state.favorites %} <button @click:=state.items.push payload="{{ favorite }}" >{{ favorite|capfirst }}</button> {% endfor %} </Template> <State items:=[] favorites:='[ "zucchini", "oatmeal", "oranges", "apples", "candy", "bread" ]' ></State>
  1. Examine this next code. In this iteration, the same technique is reapplied to adding to this "item favorites" list. You can think of it as two shopping lists: The list itself and favorites, where the user adds to favorites, and favorites adds to the shopping list.
<Template> <h3>Shopping list | {{ state.items|length }}</h3> <p>{{ state.items|join }}</p> <hr /> <h4>Favorites</h4> {% for favorite in state.favorites %} <button @click:=state.items.push payload="{{ favorite }}" >{{ favorite|capfirst }}</button> {% endfor %} <hr /> <input [state.bind] name="text" style="width: 60%" /> <button @click:=state.favorites.push payload="{{ state.text }}" >+</button> </Template> <State items:=[] favorites:='[ "oatmeal" ]' text="" ></State>

This next iteration on the code will be bigger.

This section mentioned "ergonomics" earlier, though from a coder or designer perspective. Perhaps it's very obvious, but the more important ergonomics is that the page itself is usable, and users (e.g. non-coders, website visitors, etc using the page) can understand how to use the app from a user perspective.

For this last set of tweaks, we'll learn HTML and Modulo features that make it easier to write more pleasant applications. First, we'll use a feature of HTML: The placeholder="Add to favorites" attribute, that lets us add a "default placeholder" in HTML. Then, we'll use the Modulo template tag {% empty %} to our {% for %} loop for a user-friendly message when we have an empty list. Finally, we'll add two if-statements: One to stop empty text, and the to warn users trying to add duplicates. For simplicity, we'll just use the browser's built-in tooltip with a title="..." attribute on an HTML abbreviation tag (abbr).

Examine the following final code transformation:

<Template> <h3>Shopping list | {{ state.items|length }}</h3> <p>{{ state.items|join }}</p> <hr /> <h4>Favorites</h4> {% for favorite in state.favorites %} <button @click:=state.items.push payload="{{ favorite }}" >{{ favorite|capfirst }}</button> {% empty %} <em>(None yet! Use form below.)</em> {% endfor %} <hr /> <input [state.bind] name="text" placeholder="Add to favorites" style="width: 60%" /> {% if state.text %} {% if state.text not in state.favorites %} <button @click:=state.favorites.push payload="{{ state.text }}" >+</button> {% else %} <abbr title="{{ state.text }} already in favorites."> [ ! ] </abbr> {% endif %} {% endif %} </Template> <State items:=[] favorites:='[]' text="" ></State>
Comprehension Question

What good are click events for?

  • Answer: Most interactive applications rely on click events to have user interactivity via mouse.


Developer Console? - When using Modulo, you should have the JavaScript Console open on your web browser. This is available by right clicking (or Command Clicking for macOS users), and selecting "Inspect". Then, on the right side or bottom (or in another location, with customization), there should be a tab that says Console. Click on this one. You should see a big, friendly Modulo logo.

While Modulo is designed to be a handy little tool for web developers even without use of embedded JavaScript or Script parts, sometimes you just need access to that extra power of custom JavaScript code.

Learning Tips
  • Tip 1: When developing with Modulo, especially if you are working with JavaScript, remember to keep your JavaScript Console open, so you know if there are errors!

  • Tip 2: This tutorial only covers a tiny bit of how to add some JavaScript to your page. It does not go into much detail about the language. For this, consider a different tutorial, such as MDN's JavaScript Basics, MDN's Learn JavaScript tutorial collection, or JavaScript.info.

The Script CPart

To add JavaScript, use the Script CPart. This CPart will execute the JS code contained within once, immediately upon loading the component. See this example:

<Script> console.log("Hello JavaScript world!"); </Script>

Event directives in detail Let's break down the event directive once again: @click:=script.sayHello. First, note the at-sign: @. This is "syntactic sugar" for the [component.event] directive. This will attach a "click" event listener to the given element when that element is first mounted (i.e. displayed on the screen), and remove the listener if it leaves. In this case, we are using a := style "data prop" style assignment, to assign the click event to point to the sayHello function of the Script CPart. All functions defined in a Script CPart will automatically be "exported" and available to click events, or in dataprops in general.

In this above example, the Script CPart will execute that JS code once, as soon as it's loaded, causing the "console.log" to log that message to the web browser's Developer Tools JavaScript Console exactly once.

Attaching click events

Typically, it's more useful to execute code when a user performs an action. To do this, we must place the "console.log" into a function:

<Script> function sayHello() { console.log("Hello JavaScript world!"); } </Script>

Then, attach a "click" event directive to a HTML tag, such as, for example, a button element:

<button @click:=script.sayHello>Click me</button>

Now, whenever a user clicks on the button, it will run the "sayHello" function, logging the text into the JavaScript console.

Try it now
<Template> <button @click:="script.doLog">console.log a message</button> </Template> <Script> console.log("COMPONENT GOT LOADED!"); function doLog() { console.log("Hello Modulo Scripting World!"); } </Script>
  1. Bring up the console: Press Control+Shift+J (Linux, Windows) or Command+Option+J (macOS) on your keyboard to open the Console. Alternatively, you can right-click with your mouse and select "Inspect", and then go to the Console tab.
  2. Do you see the "COMPONENT GOT LOADED!" text displayed in the console? It is displayed once every time the component is loaded. By clicking "RUN", you can "reload" the component, causing that message to show (or count up) again.
  3. Try now clicking on the button in the preview on the right. Do you see how every time you click it shows (or counts) the text of the console.log in the console?
  4. Extra: Any number of functions can be defined in a Script CPart. Practice writing your own function that console logs a different message, and then attaching it to a new button (or the existing button).
  5. Extra: The "event" directive supports any event. Try changing "@click" to "@mouseover", and then move your mouse over the button (without clicking).

Interacting with state

The Script CPart is like the Template CPart in one way: You get variables referencing the other CParts. Within functions defined in the Script CPart, variables will be available representing the other CParts that have been defined in the Component. As with the Template CPart, the most useful variables are state, with the current data in State CPart (the "data" Object), and props, with the value of the attributes that were passed to this component.

Remember our "Holmes-style" detective work we did in the previous section? We looked at a button which incremented a value when clicked. The JavaScript code to increment a variable is num++, and for state data it can be: state.num++. Also, by default, components will rerender after every event that you are listening to. With that in mind, examine the code of the Hello button:

<Template> <button @click:="script.doCountup">Hello {{ state.num }}</button> </Template> <State num:=42 ></State> <Script> function doCountup() { state.num++; } </Script>

By clicking on the button, it will increment the state value. Since the component will rerender after the click, it will then change the DOM to show the new number.

With the power of JavaScript, you can do all manner of things with the Script tag. The Examples page has all sorts of examples of more complicated apps and applications. The typical use of a Script tag, thus, is to create custom logic that manipulates or "puppets" the state, which in turn is what controls the rendering of the component's HTML code by the Template CPart.

Keep in mind that the Script CPart is intended to be limited. Serious JavaScript development should be split into separate JS files, or defined as custom CParts. Thus, think of the Script CPart as more "filling in the gaps" between CParts, which should do most of the heavy lifting (e.g. asynchronous code, complicated API calls or data transformation, etc).

Try it now

See if you can understand how this classic To-Do app operates, which interacts with state in two different ways (clearing an input, and pushing to a list).

<!-- The classic "To-Do" app in Modulo. The State CPart "binds" the input so it can be to be cleared or retrieved, and keeps track of the list. --> <Template> <ol> {% for item in state.list %} <li>{{ item }}</li> {% endfor %} <li> <input [state.bind] name="text" /> <button @click:=script.addItem>Add</button> </li> </ol> </Template> <State list:='["Milk", "Bread", "Candy"]' text="Coffee" ></State> <Script> function addItem() { state.list.push(state.text); // add to list state.text = ""; // clear input } </Script>
Comprehension Question

This To-Do app could be done without a Script tag - we were building similar apps just before adding events that went directly to state.list.push. Why would you choose one over the other?

  • Answer: As with other questions - whatever is easiest! Typically, avoid using a Script until you have to, since this requires a lot more care, since it's more flexible than just directly attaching an event, and thus has more opportunities for bugs or confusing code. Often, you might encounter something that cannot be done directly. Then, that's time for the Script CPart and custom JavaScript.

Custom Directives

New to JavaScript? You probably won't have much need for this. Feel free to skip this last section!

DOM Methods? What DOM methods are there? All "DOM elements" (p, h1, etc) also have methods or different "verbs" or "commands" you can do to it. These enable different direct modifications to the DOM, and are how Modulo itself implements many of its features. Typically, you should just use Templating, and only do direct DOM manipulation as a last resort. However, for a full reference, you can refer to MDN's documentation: DOM Introduction, DOM-Node reference

Sometimes you need to be able to directly modify the browser's DOM (document structure) at certain spots in your component. This is where writing your own directives comes into play. All the directives built-in directives ([state.bind], events, and data props), are built using JS functions or methods that activate when certain attributes are found on the document. You can leverage the same system for your own to do similar direct DOM manipulation (e.g. attaching events or manually modifying its content).

For example, examine the following code:

<div [script.ready]> Hey! </div>

Note how in the same format as [state.bind], we wrote [script.ready]. This will invoke the corresponding readyMount function when the element appears, and readyUnmount when it is removed from the page:

function readyMount({ el }) { console.log('The element is ready:', el); el.innerHTML = '<h1>Hello DOM world!</h1>'; } function readyUnmount({ el }) { console.log('The element is about to go away:', el); }

Note that the naming is important: the directive name must be all lowercase, and the function must end with either Mount or Unmount.

Try it now

One common use of directives might be to focus a particular input. Try uncommenting the el.focus() line of code (that is, removing the // prefixing it), and see what happens when you click RUN:

<Template> <label>Top: <input /></label> <label>Middle: <input [script.focus] /></label> <label>Bottom: <input /></label> </Template> <Script> function focusMount({ el }) { el.value = 'Ready to type:'; // el.focus(); } </Script>
Comprehension Question

What are uses of custom directives?

  • Answer: When core Modulo features are not enough, and you need to directly use the browser's DOM methods.

When you should do direct DOM manipulation with directives?

  • Answer: Only do direct DOM manipulation as a last resort, such as when you run into something that Modulo seems incapable of, or when you are are combining Modulo with another framework or tutorial that operates with direct DOM references

Part 5: Summary

We learned about events, and how to attach various operations to click events. We learned a little bit about attaching JavaScript-powered script tags to our components, and then activating functions via either events or directives.

Key terms

  • Events - Browsers generate events constantly when users interact with the page
  • Event listening - Listen to events to activate certain methods when they occur
  • methods - All types of data has "methods" attached to it, enabling different modifcaations to happen
  • Script - CPart that enables embedding of arbitrary JavaScript code, and allowing for easy access to CPart interface, and exposing JS functions to be attached as events
  • Directive - A special type of HTML attribute that "hooks in" functionality to otherwise plain HTML elements.
    • @click (shortcut for [component.event]) - attach event listener to element
    • [script.dostuff] - custom defined directives for accessing DOM API directly

Next step

That's all for the Ramping Up with Modulo tutorial! However, that's far from all for Modulo in general. Only some of Modulo's features have been covered by this tutorial, but it's merely the first in a series.

What's next for you?

  1. 👷 🏗️ 📦 Building Apps with Modulo 👷 🏗️ 📦 - Continue the tutorial series and build a something bigger!
  2. Continue perusing the full Modulo Documentation to focus learning on a particular topic