Display dynamic html content like an epub/ebook, without converting html to epub format?

Question

I want to create a responsive, mobile optimized reading experience similar to an epub/ebook reader, like the Kindle app, or iBooks, using dynamic html as the source.

Imagine a long article or blog post that requires a lot of vertical scrolling to read, especially on a small mobile device. What I would like to do is break the long page into multiple full-screen sections, allowing the user to use left/right navigation arrows and/or the swipe gesture to "page" through the article.

There are many JS libraries available that can create a "slide show" or "carrousel" of pre-defined slides (using divs or other container elements). But I want the text and html content to dynamically re-flow to fit any device viewport and still be readable... just like an epub/ebook user interface, like the Kindle app or iBooks. So, for the same article, there would be many more "pages" on a phone than there would be on a tablet or desktop viewport, and those "pages" would need to be dynamically created/adjusted if/when the viewport size changes (like switching from portrait to landscape on a mobile device).

Here is an example of a javascript .epub reader: epub.js

... notice the responsive behavior. When you resize your viewport, all the text re-flows to fit the available space, increasing or decreasing the total number of "pages". The problem is that epub.js requires an .epub file as its source.

What I want is the same user interface and functionality for an html page.

I have searched and searched for some kind of library that can do this out of the box, but haven't been able to find anything.

I realize that I could use a conversion script to convert my html page into an .epub file, and then use epub.js to render that file within the browser, but that seems very round-about and clunky. It would be so much better to mimic or simulate the .epub reader user experience with html as the direct source, rendering/mimicking a client side responsive ebook user experience.

Does anyone know if something like this already exists, or how I could go about building it myself?

The crucial functionality is the dynamic/responsive text-reflow. When the viewport dimensions are reduced, the text/content needs to reflow to the next "page" to avoid any need for vertical scrolling. I don't know how to do this efficiently. If I were to code it myself, I might use something like the jQuery Columnize plugin, setting all columns to width: 100vw; height: 100vh, so that each column is like a "page", and then figuring out how to create a swipe UI between those "pages".

Any help is much appreciated!

Answer 1

This becomes very difficult if the html page is complex, eg with precisely positioned elements or images. However if (as in the epub.js example) the content consists only of headings and paragraphs, it is achievable.

The basic idea is to progressively add content until just before the page overflows. By keeping track of where we start and stop adding content, clicking to the next page is a case of changing the page start to the previous page end (or vice versa if you're going back).

Process for reshaping content into pages

Let's assume you have all your content in one long string. Begin by splitting all the content into an array of words and tags. It's not as easy as splitting by whitespace as whitespace between < and > should be ignored (you want to keep classnames etc within each tag). Also tags should be separated as well, even if there is no whitespace between the tag and a word.

Next you need a function that checks if an element's contents overflow the element. This question has a copy-paste solution.

You need two variables, pageStart and pageEnd, to keep track of what indexes in the array are the beginning and end of the current page.

Beginning at the index in pageStart you add elements from the array as content to the page, checking after each add whether or not the contents overflow. When they do overflow you take the index you're up to, minus 1, as the index for pageEnd.

Keeping tags across page breaks

Now if all's ticketyboo then this should fill the page pretty well. When you want to go to the next page set your new pageStart as pageEnd + 1 and repeat the process. However there are some issues that you may want to fix.

Firstly, what happens if the page overflows in the middle of a paragraph? Strictly speaking the closing tag, </p>, is not required in HTML, so we don't need to worry about it. But what about the start of the next page? It will be missing an opening tag and that is a major problem. So we have make sure we check if the page's content begins with a tag, and if it doesn't then we get the closest opening tag prior to the current pageStart (just step back along the array from pageStart) and add it in before the rest of the content.

Secondly, as shown in the example, if a paragraph continues onto the next page, the last line of the current page is still justified. You need to check if pageEnd is in the middle of a paragraph and if so add syle="text-align-last:justify;" to the opening tag of that paragraph.

Example implementation

A pen showing all this in action is at https://codepen.io/anon/pen/ZMJMZZ

The HTML page contains all content in one long element. The content is taken directly from the container #page and reformed into pages, depending on the size of #page. I have't implemented justifying the last line if a page break occurs within a paragraph. Resize the #page element in the css and see how the content resizes itself - note that since the page size is fixed you'll have to use click forward and back to trigger a recalculation. Once you bind the page size to the window size, recalculating pages on the fly simply involves adding a resize event listener to the window that calls fillPage.

No doubt there are numerous bugs, indeed it will sometimes display things incorrectly (eg skipping or repeating words at the beginning or end of a page), but this should give you an idea of where to start.

Answer 2

The idea is to have a div that will contain the whole text (let's call this div #epub_container). Then, you will have a div with the same size of the page viewport (let's call it #displayer) and it will contain #epub_container.

#displayer will have css overflow:hidden. So when the site loads, it will only show the first page, because the rest of the #epub_container will be hidden. Then you need a page navigator to increment/decrement the page number. When the page number changes, we will move the top offset of the #epub_container based on that.

This is the jQuery function:

function move_to_page() {
    var height = window.innerHeight;
    var width = window.innerWidth;

    var $displayer = $('#displayer');
    var offset = $displayer.offset();
    $displayer.height(height - offset.top - 5);

    var $epub = $('#epub_container');
    var offset_top = offset.top - $displayer.height() * m_page;
    $epub.offset({top: offset_top, left: offset.left});
}

JSFiddle

EDIT: call move_to_page() after the text reflow in order to recompute the pages.

Answer 3

Take a look at this repository on GitHub. Otherwise, you can create a one-page website with many sections, each one as high as the viewport, by using only CSS (demo):

.section { height: 100vh; }

or by using JavaScript, adding an anchor to each section to navigate between them, and applying a responsive unit (my demo) for the text of each section, to adapt it on resize... Something like this:

var curr_el_index = 0;
var els_length = $(".container").length;

$(".next_section").on("click", function(e) {
  curr_el_index++;
  if (curr_el_index >= els_length) {
    curr_el_index = 0;
  }
  $("html, body").animate({
    scrollTop: $(".container").eq(curr_el_index).offset().top
  }, 300);
  return false;
});

$(".previous_section").on("click", function(e) {
  curr_el_index--;
  if (curr_el_index < 0) {
    curr_el_index = els_length - 1;
  }
  $("html, body").animate({
    scrollTop: $(".container").eq(curr_el_index).offset().top
  }, 300);
  return false;
});

  * {
    border: 0;
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    -moz-box-sizing: border-box;
    -webkit-box-sizing: border-box;
  }
  body {
    background-color: #1a1a1a;
  }
  section {
    height: 100vh;
    background-color: #eee;
    border: 2px solid red;
    font-size: 6vw;
  }

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<section class="container">Section 1 <a href="#" class="previous_section">Previous</a> <a href="#" class="next_section">Next</a></section>
<section class="container">Section 2 <a href="#" class="previous_section">Previous</a> <a href="#" class="next_section">Next</a></section>
<section class="container">Section 3 <a href="#" class="previous_section">Previous</a> <a href="#" class="next_section">Next</a></section>
<section class="container">Section 4 <a href="#" class="previous_section">Previous</a> <a href="#" class="next_section">Next</a></section>
<section class="container">Section 5 <a href="#" class="previous_section">Previous</a> <a href="#" class="next_section">Next</a></section>

EDIT #1

An idea of algorithm, that come from a my codepen, that uses the same jQuery plugin:

1. Create your reader layout, copying the whole text in it
2. Use this jQuery plugin to check the text inside the viewport (demo)
3. Count the number of characters/WORDS with "Onscreen" label in the viewport (a references)
4. Split the whole text in a list containing as many characters/WORDS as there are in the "Onscreen" label
5. Create a section for each element of the obtained list, filling each section with the relative text; the number of elements of the list gives you the number of pages (sections) of the whole text. You may navigate between sections like above
6. On resize event, redo [2-5] algorithm steps

Cheers