Your excitement should be growing as finally, you will stop making play pages and actually build a self-contained digital version of a text you may already know (or will see soon in your academic career), the General Prologue of The Canterbury Tales—or at least the first 18 lines. Here they are, in their late 14th century Middle English grandeur:

Whan that Aprill, with his shoures soote
The droghte of March hath perced to the roote
And bathed every veyne in swich licour,
Of which vertu engendred is the flour;
Whan Zephirus eek with his sweete breeth
Inspired hath in every holt and heeth
The tendre croppes, and the yonge sonne
Hath in the Ram his halve cours yronne,
And smale foweles maken melodye,
That slepen al the nyght with open ye
(So priketh hem Nature in hir corages);
Thanne longen folk to goon on pilgrimages
And palmeres for to seken straunge strondes
To ferne halwes, kowthe in sondry londes;
And specially from every shires ende
Of Engelond to Caunterbury they wende,
The hooly blisful martir for to seke
That hem hath holpen, whan that they were seeke.

In this chapter, you will create a webpage that glosses these first 18 lines. That is, it prints them, and then it turns every word that might not be clear into a link the user can click on. And when the user does click on such a word, the modern version of that word appears in a box below the text.

Building a page for the Prologue

First, you should make a link to the new page from your old page. Open up index.html in Atom, and add this below the <h1> tag:

<h2><a href="prologue.html">General Prologue</a></h2>

Now, create a new file in your project called prologue.html Paste into it this basic structure:

<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>General Prologue</title>
    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css" integrity="sha384-rwoIResjU2yc3z8GV/NPeZWAv56rSmLldC3R/AZzGRnGxQQKnKkoFVhFQhNUwEyJ" crossorigin="anonymous">
    <link rel="stylesheet" href="prologue.css">
  </head>
  <body>
    <div class="container">
      <h1>The General Prologue of <em>The Canterbury Tales</em></h1>
      <div id="intro">
        <p>Welcome to the first 18 lines of Chaucer’s “General 
          Prologue.” If you don’t recognize a word, just click 
          on it, and a gloss will appear below.
        </p>
      </div>
      <div id="prologue">
      </div>
      <div id="glosses">
      </div>
    <script src="https://code.jquery.com/jquery-3.2.1.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/tether/1.4.0/js/tether.min.js" integrity="sha384-DztdAPBWPRXSA/3eYEEUWrWCy7G5KFbe8fFjk5JAIxUYHKkDx6Qin1DkWx51bBrb" crossorigin="anonymous"></script>
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/js/bootstrap.min.js" integrity="sha384-vBWWzlZJ8ea9aCX4pEW3rVHjgjt7zpkNpZk+02D9phzyeVkE+jo0ieGizqPLForn" crossorigin="anonymous"></script>
    <script src="prologue.js"></script>
  </body>
</html>

Note lines 8 and 26. They load not styles.css and scripts.js, but, rather, prologue.css and prologue.js. If you want to create a prologue.css and populate it with your favorite styles, go ahead. prologue.js, however, is the focus of this chapter. So create a new file in Atom called prologue.js and paste in these two jQuery commands that should already look rather familiar to you:

$("#prologue").html("<p>The text of the Prologue will go here.</p>");
$("#glosses").html("<p>The glosses will go here.</p>");

Save and load prologue.html in the browser. The text in the jQuery commands should appear on prologue.html. If it does, commit.

Turning the Prologue into data

It could be possible to write an interactive version of the Prologue (that is, with links) in HTML, but that would involve a lot of repetition. Programmers hate repetition, so think for a moment about what the Prologue would look like as a dataset in JavaScript. What are our two data types for collections of information? Arrays and Objects. Are 18 lines of poetry more like an array or an Object? Both would work, for different reasons, but an array will be simplest.

We can think of the first 18 lines as an array that is 18 elements long, with each element being its own line, something like:

let prologueText, line1, line2, line3, line17, line18;
prologueText = [line1, line2, line3, line17, line18];

Then each line could be an array of the words (defined as things between spaces) in that line, so that:

let line1;
line1 = ["Whan", "that", "Aprill,", "with", "his", "shoures", "soote"];

In this way, prologueText would be an array of arrays. That sounds like a good way to do things, but I don’t like the line array as a line of strings. It would be better if it were an array of Objects, or word-Objects, like this:

let line1;
line1 = [{text: "Whan"}, {text: "that"}, {text: "Aprill,"}, {text: "with"},
        {text: "his"}, {text: "shoures"}, {text: "soote"}];

Now you can sort of imagine using the .map() method like this:

let line1TextArray;
line1TextArray = line1.map(function(word){
  return word.text;
});

The .map() creates a new array out of the array of word-Objects, and this new array is just the .text property of each Object, or, a string. Then we use the .join() method on line1TextArray to turn the array into one single string, separated by spaces. Put it all together in prologue.js, and:

$("#glosses").html("<p>The glosses will go here.</p>");
let line1, line1Text; // don’t need the intermediate step of line1TextArray
line1 = [{text: "Whan"}, {text: "that"}, {text: "Aprill,"}, {text: "with"},
        {text: "his"}, {text: "shoures"}, {text: "soote"}];
line1Text = line1.map(function(word){
  return word.text;
}).join(" ");
$("#prologue").html("<p>" + line1Text + "<br /></p>");
// <br /> makes a line break, which will come in handy when we have many
// lines.

Type the above into prologue.js, save, and reload. Now the first line of the Prologue should appear on the page. If it does, commit. Time to increase the complexity. Are you ready?

The Wikipedia page for the General Prologue provides a word-for-word translation into Modern English. So let’s add a property, .modern, to each word-Object that includes its modern version:

line1 = [{text: "Whan", modern: "When"}, {text: "that"}, {text: "Aprill,",
        modern: "April,"}, {text: "with"}, {text: "his"}, {text: "shoures",
        modern: "showers"}, {text: "soote", modern: "sweet"}];

This way, we can access the word.modern property and send it, as a gloss, to the #glosses entity at the bottom of the page. But that takes a little ingenuity.

Events in JavaScript

When talking about webpage design, whenever someone says something like “when a user does something, we want something to happen,” they’re usually talking about JavaScript. JavaScript and jQuery especially are very good at handling these situations, which are called events. There are several such events that jQuery recognizes, but we’ll stick to one important one, click. The jQuery method associated with clicking, $("").click(), works on any visible HTML element that gets selected by the jQuery selector, but we want it to work on individual words that have modern glosses.

Conceptually, this may be a bit tricky, so I’ll slow down and spell out the steps here that we’ll follow:

  1. As things stand now, we have a single string getting printed to #prologue that includes the first line of the Prologue.
  2. We want to break that line back up into individual word-Objects.
  3. If the word-Object has no .modern property, we print its .text property as is.
  4. If it does, we want to surround the .text property in <a> tags, so that it becomes a link.
  5. When we click on the link, we want the .modern property to get printed in #glosses.

The real final step, of course, will be to do this for all 18 lines, but let’s stick to one line for now.

The first step is straightforward. Remember, we are dealing with word-size chunks of data to begin with, so you just have to get rid of that .join() method and iterate over the array to build up the single line of text, instead:

$("#glosses").html("<p>The glosses will go here.</p>");
let line1, line1Text; // don’t need the intermediate step of line1TextArray
line1 = [{text: "Whan", modern: "When"}, {text: "that"}, {text: "Aprill,",
        modern: "April,"}, {text: "with"}, {text: "his"}, {text: "shoures",
        modern: "showers"}, {text: "soote", modern: "sweet"}];
// Create a blank string that opens two tags.
line1Text = "<blockquote><p>";
line1.forEach(function(word){
  // Add in the word-Object’s .text property plus a space.
  line1Text = line1Text + word.text + " ";
});
// Break the line and close the two tags.
line1Text = line1Text + "<br />(line 2 would go here)</p></blockquote>";
$("#prologue").html(line1Text);

Nothing changes as far as the look of the webpage (if you save and reload), but using that .forEach() method means that you expose the array to the potential for an if statement. Looking just at that block:

line1.forEach(function(word){
  // Define a variable that will be the entirety of a single
  // word-sized chunk of information.
  let wordString;
  wordString = word.text;
  // Test to see if the .modern property exists.
  if (word.modern){
    // If it does, surround wordString in an <a> tag.
    wordString = "<a href='#'>" + wordString + "</a>";
  }
  // Add wordString plus a space to the line1Text.
  line1Text = line1Text + wordString + " ";
});

Save and reload. Now the words “Whan,” “Aprill,” “shoures,” and “soote” should appear like links. If they do, commit. But if you click on them, nothing happens. Here’s where the jQuery .click() method becomes our friend. At the bottom of prologue.js, add:

$("#prologue a").click(function(){
  $("#glosses").append("<h2>You clicked on a word!</h2>");
});

The jQuery selector, $("#prologue a"), is selecting every <a> tag inside #prologue. With the click() method, it says to execute a function whenever the user clicks on an <a> tag inside #prologue. And that function appends a string, “You clicked on a word!” to #glosses. Save, reload, and start clicking on the words in the Prologue.

We have one more step, which is to have the gloss be printed, not “You clicked on a word.” But how can we tell jQuery what the value of a word-Object’s .modern property is? This is tricky, so let’s break it up into two pieces:

  1. We want to send word-specific information to #glosses.
  2. We want that information to be the .modern property.

Let’s just send the word itself to #glosses, to fulfill the first part of this step. This requires making use of the $( this ) selector we saw last chapter that lets a jQuery method get information about the selected Object:

$("#prologue a").click(function(){
  // Define the text and the word that was clicked.
  let glossText, clickedWord;
  clickedWord = $( this ).text();
  glossText = "<h2>You clicked on the word: " + clickedWord + "</h2>";
  $("#glosses").html(glossText);
});

Save and reload. Note that the .text() method, when called without parameters, gets the text. When called with parameters, it sets the text to the parameter. Unfortunately, we can’t do something like $( this ).modern to get the .modern property, though that would be pretty cool. Can you see why?

Instead, you have to feed the <a> tag some hidden data that you can then use jQuery to harvest. Here, you should make use of data attributes, which are custom, on-the-fly attributes you set in HTML. So make one, called data-modern.1 Now change the forEach loop to add the data-attribute:

line1.forEach(function(word){
  let wordString;
  wordString = word.text;
  if (word.modern){
    // Add word.modern as a data attribute to the <a> tag.
    wordString = "<a href='#' data-modern='" + word.modern + "'>" + wordString + "</a>";
  }
  line1Text = line1Text + wordString + " ";
});

Save and reload. To make sure it worked correctly, use the Element inspector (a tab near the console tab in the browser’s developer tools) to see if the HTML around the word “Whan” looks like this:

<a href="#" data-modern="When">Whan</a>

There are a lot of places to mess this up above, which is why copying and pasting chunks of code is sometimes a good idea. Of course, it’s also valuable to have to find your mistakes. One possible mistake is forgetting that single little ' after word.modern. If everything looks good, go ahead and commit.

And for the final piece of the final step, we need to get the information in the data-modern attribute into jQuery. Easy. Just use the $("").data() method:

$("#prologue a").click(function(){
  let glossText, clickedWord, modernWord;
  clickedWord = $( this ).text();
  // .data("modern") looks for the data-modern HTML attribute.
  modernWord = $( this ).data("modern");
  glossText = "<h2>You clicked on " + clickedWord + ", which means " + modernWord +"</h2>";
  $("#glosses").html(glossText);
});

Save and reload. If clicking on the words gives the modern word at the bottom, then go ahead and commit. You’re done with this part of the chapter.

JSON

You’ve done a lot in this chapter, but it’s remarkable how much builds on the steps you already know. We’re not doing anything more complicated than using arrays, Objects, and some fancier methods like .data(). There may be conceptual hurdles, however, which is why it’s worthwhile to make sure you understand how everything works above before we finish this chapter, especially since one exercise requires you to expand on what we’ve built together.

Next, this might seem like a lot of work for just one line of Chaucer! And if it were just the one line, I would agree. Luckily, it’s possible to load all 18 lines at once as one big JavaScript Object, so we can have the whole first 18 lines of the General Prologue appear on our page.

JSON stands for “JavaScript Object Notation,” and it’s a way to transport complex data using a syntax familiar to JavaScript. Concretely, that means that a JSON Object is an Object that often has an array of other Objects inside, which might have arrays or other Objects inside them. We can expand on the data structure we already set for line1 above, and imagine something like this:

let prologueObject;
prologueObject = {
  lines: [ // .lines is an array of lines
    [ // this bracket opens the line 1 array, like above
      {
        text: "Whan",
        modern: "When"
      },
      {
        text: "that"
      }
      // ...
    ], // this closes the line 1 array
    [ // this opens the line 2 array
      // ...
    ] // closes line 2
    // ...
  ] // closes the .lines property
} // closes prologueObject

As you can imagine, having to type that out would be a nightmare. Luckily, I’ve already done it for you. Open up this file in a new tab and look at it. You can see that it looks like a regular JavaScript Object except that the properties are strings, as well. That is, instead of {text: "that"}, we get {"text": "that"}. Now we have to let prologue.js know about this file.

Async

Much of the work we do with JavaScript is asynchronous, or async, for short. So far, all of our programming has been step-by-step. Do this, then do that, then do this, then do that. But the real world doesn’t really work that way, and the real world includes dealing with the internet. Maybe the server that is hosting our JSON file is slow. Maybe the file is so huge it takes a while to download it. Do we really want to wait while the whole file downloads, leaving our webpage unresponsive?

You already know I love burritos, but let’s think of this in terms of making pasta. There are three big steps to making pasta: making the sauce, boiling the pasta, and mixing them together. So let’s imagine a function:

let makeAPastaDinner;
makeAPastaDinner = function (){
  makeTheSauce(); // includes chopping vegetables and simmering
  boilThePasta(); // includes heating up the water
  mixTheSauceAndPasta();
};

By the time we got to mixTheSauceAndPasta(), the sauce would be cold! Imagine if we had to finish simmering the pasta sauce before we could start on the pasta itself. Tragedy! Disaster! Worse, we could invert them, so that we add cold, soggy pasta to sauce. Garbage!

Instead, it’d be better if we could somehow write the function so that we can start makeTheSauce() but, while it’s still happening (say, the sauce is simmering), we start boilThePasta().

That’s cooking async. And we do stuff async constantly in our daily lives. Software should be similar. In JavaScript, some functions and methods are async, which means they do their thing while, in the meantime, the rest of the functions happen. This asynchronous activity is done via callback functions, which are functions that happen only once the calling function is done. To continue with the pasta analogy, let’s get a bit more discrete:

let makeAPastaDinner;
makeAPastaDinner = function (){
  prepareSauceIngredients(function(){ // This function is the callback
    simmerSauce(function(){  // another callback
      mixTheSauceAndPasta();
    });
    boilThePasta();
  });
};

The first step is prepareSauceIngredients(). When that finishes, it executes its callback, which executes simmerSauce() and boilThePasta(), meaning that the boiling and simmering are happening at the same time. Only once the simmering is done does it call its callback, to mixTheSauceAndPasta().

In short, dealing with asynchronous functions means that sometimes the order things are written in your JavaScript file are not the order in which they are done. And jQuery’s method to get JSON Objects from the internet can be confusing in its asynchronicity.

Finishing up by combining async JSON with the General Prologue.

Let’s make sure we’re all on the same page as we turn into this last quarter lap. Your prologue.js file should look like this, more or less. I’ve taken out the comments and added three new ones.

// 1. Set the content of #glosses.
$("#glosses").html("<p>The glosses will go here.</p>");
// 2. Set the content of #prologue.
let line1, line1Text;
line1 = [{text: "Whan", modern: "When"}, {text: "that"}, {text: "Aprill,",
        modern: "April,"}, {text: "with"}, {text: "his"}, {text: "shoures",
        modern: "showers"}, {text: "soote", modern: "sweet"}];
line1Text = "<blockquote><p>";
line1.forEach(function(word){
  let wordString;
  wordString = word.text;
  if (word.modern){
    wordString = "<a href='#' data-modern='" + word.modern + "'>" + wordString + "</a>";
  }
  line1Text = line1Text + wordString + " ";
});
line1Text = line1Text + "<br />(line 2 would go here)</p></blockquote>";
$("#prologue").html(line1Text);
// 3. Wait around for the user to click on an <a> tag inside #prologue
// and then change the content of #glosses.
$("#prologue a").click(function(){
  let glossText, clickedWord, modernWord;
  clickedWord = $( this ).text();
  modernWord = $( this ).data("modern");
  glossText = "<h2>You clicked on " + clickedWord + ", which means " + modernWord +"</h2>";
  $("#glosses").html(glossText);
});

This works; it loads a line of text, and everything runs like we expect it to. But I want to underscore the fact that this code is actually doing three big things, as I’ve noted with the comments. Steps 1 and 3 stay the same. They don’t care about the actual text of the Prologue. Step 1 only concerns #glosses, and step 3 is just hanging out, waiting for the user to click. In other words, the action will happen in step 2. Now, the jQuery method to get a JSON file is $.getJSON(file, callback), and it takes two parameters, as you can see. The file part is easy, since you’ve been looking at it already:

$.getJSON("https://the-javascripting-english-major.org/prologue.json", callback);

The callback is a bit trickier, but let’s think it through abstractly:

  1. We have the JSON available to us as a variable for our callback called data.
  2. This data Object has a property, .lines, that is an array of lines.
  3. Each line in .lines is an array of word-Objects.
  4. Each word-Object has a .text property, and some have a .modern one.

Then look to what you already have in that second step:

  1. It defines line1, an array of word-Objects, and line1Text, a blank string.
  2. It iterates over line1 and builds up line1Text based on the properties of the word-Objects.
  3. It closes the HTML tags in line1Text.
  4. It prints the value of line1Text in #prologue.

Really all you need to do is two things: create a prologueText variable that holds the text of the whole Prologue and repeat what you’ve already got down:

$.getJSON("https://the-javascripting-english-major.org/prologue.json", function(data){ // Note the data variable!
  let prologueText; // Define the variable you didn’t need before.
  prologueText = "<blockquote><p>"; // Open the tags.
  // Now you can iterate over the data variable’s .lines property:
  data.lines.forEach(function(line){ // We get a variable, line.
    // Define a blank lineText.
    let lineText;
    lineText = "";
    // Now iterate over each line. This part should be familiar.
    line.forEach(function(word){
      let wordString;
      wordString = word.text;
      if (word.modern){
        wordString = "<a href='#' data-modern='" + word.modern + "'>" + wordString + "</a>";
      }
      lineText = lineText + wordString + " ";
    });
    // Add lineText with a line break to the prologueText.
    prologueText = prologueText + lineText + "<br/>";
  });
  // Close the prologueText tags.
  prologueText = prologueText + "</p></blockquote>";
  // Replace the content of #prologue.
  $("#prologue").html(prologueText);
}); // Close the callback function & method.

If you replace step two with this, save, and reload, huzzah! The first 18 lines of the General Prologue appear. But if you click on the words, they don’t work anymore. Nothing happens. That’s not fair! We didn’t even touch step 3. Why did it work before, but not now?

The answer is, you probably guessed, because of async. Think of the three steps as three discrete functions:

setTheDefaultGlossesValue();
setTheDefaultPrologueValue();
selectThePrologueLinksAndWaitForClicks();

Because the second function runs asynchronously, the third function looks for links in #prologue, but #prologue is still blank. So by the time the second function is done, the third has already finished its business. We need to treat the third function as a callback to the second. We need to do something like this:

setTheDefaultGlossesValue();
setTheDefaultPrologueValue(function(){
  selectThePrologueLinksAndWaitForClicks();
});

Figuring out how to do that is for homework. But here is what the final page could look like: prologue.html.

Exercises

  1. Why can’t we simply do $( this ).modern to get the .modern property?
  2. Fix the problem with the Prologue and get the glosses to appear.
  3. I added a "url" property to the JSON file. Rewrite the code for the Prologue so that the gloss also suggests taking you to Wikipedia if you like.

Foonotes

  1. Data attributes all begin with data-. ↩

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