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December 12, 2017 12:15
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War on scrolling! Paginate web pages and use arrow keys or a small UI to navigate between screens
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const $spans = [...document.querySelectorAll('*')] | |
.map($ => | |
[...$.childNodes].filter($ => | |
$.nodeType === 3 | |
) | |
) | |
.reduce((a, b) => | |
[...a, ...b] | |
) | |
.map(textNode => { | |
const $span = document.createElement('span') | |
$span.appendChild(textNode.cloneNode()) | |
textNode.replaceWith($span) | |
return $span | |
}) | |
const [[margin]] = $spans | |
.map($ => | |
$.getBoundingClientRect().left | |
) | |
.sort((a, b) => | |
a > b ? 1 : -1 | |
) | |
.reduce( | |
([last, ...previous], current) => | |
[ | |
...( | |
current === last[0] | |
? | |
[[current, ...last]] | |
: | |
[[current], last] | |
), | |
...previous | |
], | |
[[]] | |
) | |
.sort((a, b) => | |
a.length < b.length ? 1 : -1 | |
) | |
$spans.forEach($ => | |
$.replaceWith($.firstChild) | |
) | |
const pages = [...document.querySelectorAll('*')] | |
.filter($ => | |
getComputedStyle($).display === 'block' | |
&& | |
$.offsetHeight < innerHeight | |
) | |
.reduce( | |
($$, $, i) => ( | |
i && $$[$$.length - 1].contains($) | |
? | |
$$ | |
: | |
[...$$, $] | |
), | |
[] | |
) | |
.map($ => ({ | |
$, | |
top: $.offsetTop, | |
bottom: $.offsetTop + $.offsetHeight, | |
})) | |
.reduce( | |
({pages, offset}, {$, top, bottom}) => { | |
const edge = pages * innerHeight, | |
over = edge <= bottom + offset, | |
inter = edge - margin <= offset + bottom | |
&& | |
edge + margin >= offset + top | |
if(over || inter) | |
pages++ | |
if(inter){ | |
const $gap = document.createElement('div') | |
const gap = edge - top + margin | |
$gap.style.height = gap + 'px' | |
$.prepend($gap) | |
offset += gap | |
} | |
return { | |
pages, | |
offset, | |
} | |
}, | |
{ | |
pages: 1, | |
offset: 0, | |
} | |
) | |
.pages - 1 | |
document.head.appendChild( | |
Object.assign( | |
document.createElement('script'), | |
{ | |
src: 'https://unpkg.com/mithril', | |
onload: () => { | |
let page = 0 | |
Object.assign(document.body.style, { | |
overflow: 'hidden', | |
height: innerHeight * pages + 'px', | |
}) | |
const back = () => | |
m.redraw(page && page--) | |
const forð = () => | |
m.redraw(page < pages && page++) | |
document.addEventListener('keydown', ({key}) => | |
key === 'ArrowLeft' && back() | |
|| | |
key === 'ArrowRight' && forð() | |
) | |
m.mount( | |
document.body.appendChild( | |
document.createElement('div') | |
), | |
{ | |
view : () => ( | |
scrollTo(0, page * innerHeight), | |
m('div', { | |
style : { | |
background: 'hsla(0,0,100,80)', | |
position: 'fixed', | |
bottom: 0, | |
right: 0, | |
zIndex: 9999, | |
}, | |
}, | |
m('button', {onclick : back}, '<'), | |
' ', | |
m('span', page, '/', pages), | |
' ', | |
m('button', {onclick : forð}, '>') | |
) | |
) | |
} | |
) | |
} | |
} | |
) | |
) |
Revision 2
Untested attempt at addressing the bugs using latest proposed solutions. Accidentally deleted UI code — Github Gists aren't friendly on mobile.
Tweaked page counting algorithm to account for instances where the page may break naturally in the pre-existing gap between 2 blocks — in practice this will break the mechanism because A) it doesn't account for offset and B) it won't pick up on introduced gaps as a result of margin intersection.
Revision 3
Fixed the blind-coding errors but now the gaps mechanism is broken 🤔
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…So the question of how to fix #2 now is how to identify more appropriate higher order containing blocks without including unhelpfully large ones. Perhaps prioritise higher order containers by default unless they exceed viewport height?