=> clean slate software_

Pagination

This script produces a pdf-like paged document from basic HTML. For the prototype I decided to use the last draft of my ill-fated Masters thesis on the history of self-esteem. Some readers may find this content as or more interesting than the code itself. Special thanks to Timothy Verhoeven and Michael Hau for the feedback that helped shape this draft. To read it and/or see my code in action, open the following link with an up-to-date version of Firefox, Chromium or Chrome:

The History of Self-Esteem

Note: it is not written to work on Internet Explorer due to the browser’s prehistoric Javascript support. It may however work with other browsers. Although the script was specifically written to work with Firefox, slightly older versions of Firefox have a display problem: you cannot zoom in or out without modifying and sometimes hiding the text. If you wish to zoom, hit F5 afterwards to re-render the pages. Also, for anyone wishing to cite the content, the page numbers cannot be relied on for consistency. Finally, it was not designed for proper smartphone display, but relies on smartphone browsers behaving like desktop ones.

The CSS standard has long covered the display of HTML on discrete pages like a book, but implementation of this feature has been lacking. The PagedJS project has created a Javascript library to fill this gap. I studied this project in order to understand how the implementation works. I then developed a very different implementation from the perspective of functional programming. In doing so I adhered very closely to the wisdom of Luis Atencio’s Functional Programming in Javascript, the book that sold me on the functional paradigm. This book and the PagedJS project are thus the two influences reflected in my code below and warmly acknowledged.

The code mainly focuses on dividing the content across pages intelligently. I have taken great pains to prevent single lines, including headings, appearing in isolation at the tops and bottoms of pages. To my judgment, I have succeeded in making my history writing look almost as nice as the concise and declarative compositions and recursion-based machinery behind it.

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<script>

/*

The MIT License (MIT)

Copyright © 2020 Dean Lee

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

*/

//global constant values

const styleString = `
body {margin: 0; padding: 0;}
.pages {
  text-rendering: geometricPrecision;
  background-color: #555555;
  margin: 0;
  padding: 20mm 0;
}
.hiphip_page {
  box-sizing: border-box;
  width: 210mm;
  height: 297mm;
  margin-left: auto;
  margin-right: auto;
  margin-top: 0;
  margin-bottom: 20mm;
  padding: 0;
  border-width: 0;
}
.hiphip_sheet {
  background-color: #ffffff;
  box-sizing: border-box;
  border-width: 0;
  padding: 0;
  margin: 0;
  width: 210mm;
  height: 297mm;
  overflow: hidden;
}
.hiphip_pagebox {
  box-sizing: border-box;
  border-width: 0;
  margin: 0;
  width: 210mm;
  height: 297mm;
  overflow: hidden;
  display: grid;
  grid-template-columns: [left] 25mm [center] 160mm [right] 25mm;
  grid-template-rows: [header] 30mm [page] 237mm [footer] 30mm;
}
.hiphip_margin-top {
  grid-column: center;
  grid-row: header;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: 100%;
}
.hiphip_margin-top-left-corner-holder {
  grid-column: left;
  grid-row: header;
}
.hiphip_margin-top-right-corner-holder
  grid-column: right;
  grid-row: header;
}
.hiphip_margin-right {
  grid-column: right;
  grid-row: page;
}
.hiphip_margin-left {
  grid-column: left;
  grid-row: page;
}
.hiphip_margin-bottom {
  grid-column: center;
  grid-row: footer;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: 100%;
}
.hiphip_margin-bottom-left-corner-holder {
  grid-column: left;
  grid-row: footer;
}
.hiphip_margin-bottom-right-corner-holder {
  grid-column: right;
  grid-row: footer;
}
.hiphip_area {
  grid-column: center;
  grid-row: page;
}
.hiphip_page-content {
  width: 100%;
  height: 100%;
  column-fill: auto;
  column-width: 170mm;
  column-gap: 40mm;
  line-height: 1.6em;
}
.hiphip_margin-bottom-center {
  text-align: center;
  margin-top: 10%;
  margin-bottom: auto;
}
@media print {@page {margin: 0; padding 0;} .pages {margin: 0; padding: 0;} .hiphip_page {margin: 0;}}
`

const templateString = `
<div class="hiphip_page">
    <div class="hiphip_sheet">
        <div class="hiphip_pagebox">
            <div class="hiphip_margin-top-left-corner-holder">
            </div>
            <div class="hiphip_margin-top">
                <div class="hiphip_margin hiphip_margin-top-left"><div class="hiphip_margin-content"></div></div>
                <div class="hiphip_margin hiphip_margin-top-center"><div class="hiphip_margin-content"></div></div>
                <div class="hiphip_margin hiphip_margin-top-right"><div class="hiphip_margin-content"></div></div>
            </div>
            <div class="hiphip_margin-top-right-corner-holder">
            </div>
            <div class="hiphip_margin-right">
            </div>
            <div class="hiphip_margin-left">
            </div>
            <div class="hiphip_margin-bottom-left-corner-holder">
            </div>
            <div class="hiphip_margin-bottom">
                <div class="hiphip_margin hiphip_margin-bottom-left"><div class="hiphip_margin-content"></div></div>
                <div class="hiphip_margin hiphip_margin-bottom-center"><div class="hiphip_margin-content"></div></div>
                <div class="hiphip_margin hiphip_margin-bottom-right"><div class="hiphip_margin-content"></div></div>
            </div>
            <div class="hiphip_margin-bottom-right-corner-holder">
            </div>
            <div class="hiphip_area">
                <div class="hiphip_page-content"></div>
            </div>
        </div>
    </div>
</div>`

const head = document.querySelector('head');
const body = document.querySelector('body');
const headingElements = ['H1', 'H2', 'H3', 'H4', 'H5', 'H6'];
const blockElements = ['DIV', 'P', 'OL', 'UL', 'LI', 'BLOCKQUOTE', 'HR', 'H1', 'H2', 'H3', 'H4', 'H5', 'H6'];
const safetyGap = 20; // exaggerate coordinates to avoid overlap etc.

// fundamental utilities

const push = (item) => (array) => {
    array.push(item);
    return array;
}

const tail = (list) => {
    Array.prototype.shift.call(list);
    return list;
}

function pipe() { // "arguments" does not work with the lambda
    let recursion = (value, funcs) => funcs.length === 0 ? value : recursion(funcs[0](value), tail(funcs));
    return recursion(arguments[0], tail(arguments));
}

const increment = (index) => ++index;

// DOM utilities

const parentNode = (node) => node.parentNode;
const previousSibling = (node) => node.previousSibling;
const previousElementSibling = (element) => element.previousElementSibling;
const nextSibling = (node) => node.nextSibling;
const nextElementSibling = (element) => element.nextElementSibling;
const firstChild = (node) => node.firstChild;
const firstElementChild = (element) => element.firstElementChild;
const lastChild = (node) => node.lastChild;
const lastElementChild = (element) => element.lastElementChild;
const findDeepest = (childType) => (node) => !childType(node) ? node : pipe(childType(node), findDeepest(childType));
const climbToSibling = (siblingType) => (node) => siblingType(node) || isTop(node) ? node : pipe(parentNode(node), climbToSibling(siblingType));

const nearestCousin = (siblingType) => (node) => {
    let childType = siblingType === nextSibling ? firstChild : lastChild;
    let top = climbToSibling(siblingType)(node);
    let sibling = siblingType(top);
    return !sibling ? false : findDeepest(childType)(sibling);
}

const previousCousin = (node) => nearestCousin(previousSibling)(node);
const nextCousin = (node) => nearestCousin(nextSibling)(node);

const listRelatives = (relativeType) => (node) => {
    let recursion = (node, acc = []) => {
        let newAcc = push(node)(acc);
        let newNode = relativeType(node);
        return !newNode ? newAcc : recursion(newNode, newAcc);
    }
    return recursion(node);
}

const importNode = (node) => document.importNode(node, true);
const createElement = (name) => document.createElement(name);

const addClass = (className) => (element) => {
    element.classList.add(className);
    return element;
}

const setFlag = (flag) => (element) => {
    element.setAttribute(flag, 'true');
    return element;
}

const append = (node) => (dest) => {
    dest.appendChild(node);
    return dest;
}

const appendTo = (dest) => (node) => {
    dest.appendChild(node);
    return dest.lastChild;
}

const insertBefore = (reference) => (node) => {
    parentNode(reference).insertBefore(node, reference);
    return node;
}

const innerHTML = (content) => (element) => {
    element.innerHTML = content;
    return element;
}

const cloneElement = (element) => {
    let clone = element.cloneNode(false);
    setFlag('data-clone')(clone);
    if (clone.id) {
        clone.id = clone.id + '-cl';
    }
    return clone;
}

// text processing utilities

class TextSection {
    constructor(node, start, end) {
        this.node = node;
        this.start = start;
        this.end = end;
    }

    midRange (start, end) {
        return Math.floor(start + ((end - start) / 2));
    }
  
    copyFirstHalf() {
        return new TextSection(this.node, this.start, this.midRange(this.start, this.end));
    }
  
    copySecondHalf() {
        return new TextSection(this.node, this.midRange(this.start, this.end) + 1, this.end);
    }
  
    copyShiftLeft() {
        return new TextSection(this.node, this.start - 1, this.end - 1);
    }

    wrapInRange() {
        let range = document.createRange();
        range.setStart(this.node, this.start);
        range.setEnd(this.node, this.end + 1);
        return range;
    }
  
    getLeft() {
        return this.wrapInRange().getBoundingClientRect().left;
    }
  
    getRight() {
        return this.wrapInRange().getBoundingClientRect().right;
    }
}

const getNode = (textSection) => textSection.node;
const getfirstChar = (node) => new TextSection(node, 0, 0);
const getLastChar = (node) => new TextSection(node, node.data.length - 1, node.data.length - 1);

const getTextSection = (node) => {
    let end = isText(node) ? node.data.length - 1 : 0;
    return new TextSection(node, 0, end);
}

const getRectArray = (range) => {
    let pseudoArray = range.getClientRects();
    return Array.prototype.slice.call(pseudoArray, 0);
}

const wrapInRange = (node) => {
    let range = document.createRange();
    range.selectNode(node);
    return range;
}

const getRects = (element) => {
    let nodes = pipe(element, findDeepest(firstChild), listRelatives(nextCousin));
    let rectArrays = nodes.map((x) => pipe(x, wrapInRange, getRectArray));
    return rectArrays.reduce((a, b) => a.concat(b));
}

const getRight = (node) => {
    let rect = isElement(node) ? node.getBoundingClientRect() : wrapInRange(node).getBoundingClientRect();
    return rect.right;
}

// node information booleans

const isElement = (node) => node.nodeType === 1;
const isText = (node) => node.nodeType === 3;
const hasFlag = (flag) => (node) => !isElement(node) ? false : node.getAttribute(flag);
const isHeading = (element) => headingElements.some((x) => x === element.nodeName);
const isBlock = (element) => blockElements.some((x) => x === element.nodeName);
const isLi = (element) => element.nodeName === 'LI';
const isTop = (node) => hasFlag('data-top')(node);
const isMerger = (node) => hasFlag('data-merger')(node);

// misc utilities

const mark = (node) => { // for testing; beautiful way to track element traversal in pipes!
    if (isElement(node)) {  // e.g. pipe(node, mark, oFBlock)
        setFlag('x')(node);
    }
    return node;
}

const styleContent = () => document.createTextNode(styleString);
const getPageContent = (page) => page.querySelector('.hiphip_page-content');

// source preparation

const finishedMerger = (merger) => !pipe(merger, lastChild, isHeading) || !nextElementSibling(merger);
const createMerger = (element) => pipe(createElement('div'), insertBefore(element), setFlag('data-merger'), append(element));
const mergeNext = (merger) => pipe(merger, nextElementSibling, appendTo(merger), parentNode);

const mergeHeadings = (element) => {
    let recursion = (merger) => finishedMerger(merger) ? merger : pipe(merger, mergeNext, recursion);
    return !isHeading(element) ? element : pipe(element, createMerger, recursion);
}

const getSource = () => {
    let recursion = (element, acc = []) => {
        let current = mergeHeadings(element);
        let newAcc = push(current)(acc);
        let nextElement = nextElementSibling(current);
        return !nextElement ? newAcc : recursion(nextElement, newAcc);
    }
    return pipe(body, firstElementChild, recursion);
}

// page creation

const brake = (page) => { // to prevent accidental infinite page generation
    if (pages.childElementCount > 1000) {
        throw 'Page limit exceeded.';
    }
    return page;
}

const setIndex = (index) => (page) => {
    page.setAttribute('data-index', index);
    return page;
}

const getIndex = (page) => page.getAttribute('data-index');
const setPageNum = (page) => {page.querySelector('.hiphip_margin-bottom-center > div').innerHTML = getIndex(page)};
const addTemplate = () => pipe(template.content, importNode, appendTo(pages));

const setWrapper = (page) => {
    let pageContent = getPageContent(page);
    pipe(createElement('div'), addClass('wrapper'), appendTo(pageContent));
    return page;
}

const addPage = () => pipe(addTemplate(), setWrapper, brake);
const createFirstPage = () => pipe(addPage(), setIndex(1));

const newPage = () => {
    let page = addPage();
    let pageNumber = pipe(page, previousElementSibling, getIndex, increment);
    pipe(page, setIndex(pageNumber), setPageNum);    
}

const addToPage = (node) => {
    let target = document.querySelector('.hiphip_page:last-child .wrapper');
    return pipe(node, appendTo(target));
}

// overflow handling

const detectOverflow = (node) => getRight(node) > areaRight;
const containsBlock = (node) => !firstElementChild(node) ? false : pipe(node, firstElementChild, isBlock);
const firstOF = (node) => detectOverflow(node) ? node : pipe(node, nextSibling, firstOF);
const oFNode = (node) => !firstChild(node) || isLi(node) ? node : pipe(node, firstChild, firstOF, oFNode);
const oFBlock = (node) => !containsBlock(node) || isMerger(node) || isLi(node) ? node : pipe(node, firstElementChild, firstOF, oFBlock);
const findOverflow = (node) => pipe(node, oFBlock, climbToSibling(previousSibling));

const findOFHalf = (x) => {
    let firstHalf = x.copyFirstHalf();
    return firstHalf.getRight() > areaRight ? firstHalf : x.copySecondHalf();
}

const oFChar = (node) => {
    let recursion = (x) => x.start === x.end ? x : pipe(x, findOFHalf, recursion);
    let textSection = getTextSection(node);
    return isText(textSection.node) ? recursion(textSection) : textSection;
}

const pinpointOverflow = (element) => pipe(element, oFNode, oFChar);

// content division

const orphansAndWidows = (element) => {
    let rects = getRects(element);
    let oneRectPerLine = (x,i,a) => i === a.length - 1 ? true : (x.right - safetyGap) > a[i + 1].left; // safetyGap necessary to prevent accidental single widows
    let orphans = rects.filter((x) => x.right <= areaRight).filter(oneRectPerLine);
    let widows = rects.filter((x) => x.right > areaRight).filter(oneRectPerLine);
    return [orphans.length, widows.length];
}

const searchLineBreak = (current) => {
    if (current.start === 0) {
        return false;
    }
    let previous = current.copyShiftLeft();
    return current.getLeft() < previous.getLeft() ? current : searchLineBreak(previous);
}

const getPreviousLine = (textSection) => {
    if (!isText(textSection.node)) {
        return textSection;
    }
    let lineBreak = searchLineBreak(textSection);
    if (lineBreak !== false) {
        return lineBreak;
    }
    let previousSection = pipe(textSection, getNode, previousCousin, getLastChar);
    let currentSection = pipe(textSection, getNode, getfirstChar);
    return currentSection.getLeft < previousSection.getLeft ? currentSection : getPreviousLine(previousSection);
}

const handleWidows = (element, ratio) => {
    let textSection = ratio[1] > 1 ? pinpointOverflow(element) : pipe(element, pinpointOverflow, getPreviousLine);
    return isText(textSection.node) ? textSection.node.splitText(textSection.start) : textSection.node;
}

const divideElement = (element) => {
    let paragraph = isMerger(element) ? lastElementChild(element) : element;
    let ratio = orphansAndWidows(paragraph);
    return ratio[0] < 2 || (ratio[0] + ratio[1]) < 4 ? element : handleWidows(element, ratio);
}

// offcut creation

const prevLiCount = (element, acc = 0) => {
    if (!previousElementSibling(element)) {
        return acc;
    }
    let previous = previousElementSibling(element)
    if (isLi(previous)) {
        var acc = acc + 1;
    }
    return prevLiCount(previous, acc);
}

const cloneParent = (node) => {
    let parent = parentNode(node);
    let clone = cloneElement(parent);
    if (parent.nodeName === 'OL') {
        let itemNo = parent.start + prevLiCount(node);
        clone.setAttribute('start', itemNo);
    }
    return clone;  
}

const offcutCycle = (node, acc) => {
    let siblings = nextSibling(node) ? pipe(node, nextSibling, listRelatives(nextSibling)) : [];
    let clone = cloneParent(node);
    acc.appendChild(clone);
    let newChild = previousElementSibling(clone) ? previousElementSibling(clone) : node;
    appendTo(clone)(newChild);
    siblings.forEach((element) => {appendTo(clone)(element)});
    return acc;
}

const createOffcut = (node) => {
    let recursion = (node, acc = document.createDocumentFragment()) => {
        let parent = parentNode(node);
        return isTop(node) ? lastElementChild(acc) : recursion(parent, offcutCycle(node, acc));
    }    
    return isTop(node) ? node : recursion(node);
}

// high level pagination control

const pageBreak = (node) => {
    newPage();
    pipe(node,
        findOverflow,
        divideElement,
        createOffcut,
        addToPage,
        handleOverflow);
}

const handleOverflow = (node) => {
    if (detectOverflow(node)) {
        pageBreak(node);
    }
}

// execution 

const source = getSource();

const pages = pipe(createElement('div'), addClass('pages'), insertBefore(source[0]));
const style = pipe(createElement('style'), appendTo(head), append(styleContent()));
const template = pipe(createElement('template'), innerHTML(templateString));

const firstPage = createFirstPage();
const areaRight = pipe(firstPage, getPageContent, getRight) + safetyGap;

source.forEach((node) => pipe(node, setFlag('data-top'), addToPage, handleOverflow));

</script>