🎭 Scripts!

Coding Camp

Prof. Calvin

👋 Introduction

Goals

  1. Create a webpage
  2. Make it well-formed
  3. Make it stylish
  4. Make it graphical
  5. Make it interactive

Today

What?

  • We’ll animate an “eye”.
  • You can animate the spooky ghost, and I provide an example!
  • Check it out!
  • I made a number of changes to the eyes to get this to work.
    • Just check out the .html and .css files!

How?

  • We will use our third language - JavaScript
  • We can use the <script> element or include a .js file.
  • I always start my files as:
anything_calvin_does.html
<!DOCTYPE html>
<html>
  <head>
    <link rel="stylesheet" href="styles.css">
    <script type="text/javascript" src="script.js"></script>
  </head>
  <body>
    ...

Why?

  • The most used coding language of all time.
  • Runs on every computer in the world that has a webbrowser.
    • Even if the internet is out!

🌎 Hello, world!

What?

  • New language, new “Hello, world!”
  • But this time, it is interactive!
  • We will say “hello” when someone clicks.

How?

index.html
<!DOCTYPE html>
<html>
  <head>
    <script type="text/javascript" 
            src="script.js">
     </script>
  </head>
  <!-- 
  The `()` means "take an action." 
  -->
  <body onclick="hello()">
    Text.
  </body>
</html>
script.js
/* A function is a named action. */
function hello() {

    /* An alert is a text pop-up */
    alert("Hello, world!")
    
} /* Enclose the action in {} */

👀 Visually

  • Click anywhere green…
<div style="background:green;" onclick="hello()">
    Text
</div>
Text

👁 Eye-nimate

👩‍💻 Code

  • We’ll animate an “eye”.
eye.html
<!DOCTYPE html>
<html>
    <head>
        <link rel="stylesheet" 
              href="eye.css">
    </head>
    <body>
        <div id="eye">
            <div id="pupil"></div>
        </div>
    </body>
</html>
eye.css
#eye {
    position: absolute;
    border-radius: 50%;
    top: 50%;
    left: 50%;
    width: 6vmin;
    height: 6vmin;
    background: blue;
}
#pupil {
    position: absolute;
    border-radius: 50%;
    width: 3vmin;
    height: 3vmin;
    background: white;
}

👀 Visually

  • It will mostly look like this (or animate the eyes of your ghost for a challenge!):

💡 Idea

  • We will move the pupil
  • The pupil was position within the eye on the ghost using the left and top styles.
  • For example, we can move the 10vmin left and top.
    • This moves the “pupil” off the “eye” as the “eye” is only “6vmin” in radius.

📐 Geometry

  • The eye is 6x6
  • The pupil is 3x3
  • So to move the pupil all the way across the eye, move it by 3 from top and left, each.

📺 Display

  • We can follow the mouse
  • If the mouse is leftmost, the pupil should be at left:0vmin
  • If the mouse is rightmost, the pupil should be at left:3vmin
  • Helpfully:
    • JavaScript will tell us where the mouse is, and
    • JavaScript will let us easily update the style of an element.

Step 0

  • Let’s start making eye.js
  • We’ll start with the “Hello, world!” example.
script.js
function hello() {
    alert("Hello, world!")
}

Step 1 👂

  • We set the function to be performed on mouse clicks.
  • We do so using an event listener
    • A special JavaScript way to do an action whenever something happens.
script.js
function hello() {
    alert("Hello, world!")
}

document.addEventListener('click', hello);
/* "document" refers the website, 
   "click" to what you do, 
   "hello" to what JavaScript does. */

Step 2 🗺

  • Let’s see where the click occured.
  • A mouseclick is an event, so let’s “give” that event to hello by placing it within the ()
script.js
function hello(event) {
    alert(event)
}

document.addEventListener('click', hello());

👀 Visually

  • Click anywhere green…
<div style="background:green;" onclick="hello()">
    Text
</div>
Text

Step 3 🎁

  • We have to unwrap the event.
    • Lots of nonsense in there.
  • Let’s look at just the x coordinate within the webpage
    • It’s called pageX
    function hello() {
  alert(event.pageX)
}
Text

Alert 🚨

  • You may notice clicking toward the left gives smaller numbers and to the right gives bigger numbers.
    • If you didn’t try it below!
  • We can use these numbers to move the pupil!
Text

Step 4 🚶‍♀️

  • Rather than an alert, we can change the location of some HTML element.
    • Give it a name.
    • Ask JavaScript to find it.
    • Use JavaScript to change its left value to the clicked value.
    function hello(event) {
  /* Find the element by id */
  const element = document.getElementById("name");
  /* Change the "left" value of the element's style */
  element.style["left"] = event.pageX + "px"; /* x is given in "px" */
  alert(event.pageX + "px"); /* So we can see it */
}

👀 Visually

  • Click anywhere green…
    • This should work in most browsers…
    <div style="background:green;" onclick="hello()">
  <div id="name">
      Text
  </div>
</div>
Text

Step 5 📐

  • We wanted our maximum pupil movement to be 3
  • JavaScript helpful knows the maximum value for x - it is window.innerWidth
    • I just looked it up I never would’ve guessed.
  • We divide the x value by the maximum, then multiply by 3.
function hello() {
    alert(3 * event.pageX / window.innerWidth)
}
Text

Step 6 👁 on the 🏆

  • Back to the eye (and remember the CSS file!)
  • Update “pupil” not an arbitrary element.
eye.html
<!DOCTYPE html>
<html>
    <head>
        <link rel="stylesheet" 
              href="eye.css">
              
    <script type="text/javascript" 
            src="eye.js"></script>
    </head>
    <body>
        <div id="eye">
            <div id="pupil">
            </div>
        </div>
    </body>
</html>
eye.js
function hello(event) {
    /* Find the element by id */
    const element = document.getElementById("pupil");
    /* Find the new "left" value*/
    const new = 3 * event.pageX / window.innerWidth;
    /* Update */
    element.style["left"] = new + "vmin";
}

document.addEventListener('click', hello());

Step 7 ↕

  • Also do vertical movement.
eye.js
function hello(event) {
    /* Find the element by id */
    const element = document.getElementById("pupil");
    /* Find the new "x" value*/
    const x = 3 * event.pageX / window.innerWidth;
    /* Find the new "y" value*/
    const y = 3 * event.pageY / window.innerHeight;
    /* Update */
    element.style["left"] = x + "vmin";
    element.style["top"] = y + "vmin";
}

document.addEventListener('click', hello());

👀 Visually

  • It will mostly look like this (or animate the eyes of your ghost for a challenge!):

Altogether

  • This is a bit confusing.
  • Try this out altogether like so.
  • This uses mousemove rather than click (it’s more fun). 
altogether.html
<!DOCTYPE html>
<html>
  <head>
    <style>
        #eye {
          position: absolute;
          border-radius: 50%;
          top: 50%;
          left: 50%;
          width: 6vmin;
          height: 6vmin;
          background: black;
        }
        #pupil {
          position: absolute;
          border-radius: 50%;
          width: 3vmin;
          height: 3vmin;
          background: white;
        }
    </style>
    <script>
        function peep(e) {
            const p = document.getElementById("pupil");
            p.style["left"] = (3 * e.pageX / window.innerWidth).toString() + "vmin";
            p.style["top"] = (3 * e.pageY / window.innerHeight).toString() + "vmin";
        }
        
        document.addEventListener('mousemove', peep);
    </script>
        
  </head>
  <body>
      <div id="eye">
        <div id="pupil"></div>
      </div>
  </body>
</html>