A browser plugin script to identify previous / next pagination links in forums and expose them to generic keyboard navigation

feedback.js

const options = {
  duration: 600,
  easing: 'cubic-bezier(0, 0.55, 0.45, 1)',
  fill: 'both',
}

function feedback(message = 'error'){  
  const $circle = render(circle)

  $circle.animate({
    transform: ['scale(0%)', 'scale(120%)'],
  }, options)
    .onfinish = () => {
      $circle.animate({
        opacity: [1, 0],
      }, options)
    } 

  const $symbol = render(
    message === 'error' ? x : arrow
  )

  if(message === 'next')
    $symbol.firstElementChild.style.transform = 'rotate(.5turns)'

  $symbol.animate({
    transform: ['scale(200%)', 'scale(90%)'],
    opacity: [0, 1],
  }, {
    ...options,
    duration: 200,
  })
    .onfinish = () => {
      $symbol.animate({
        opacity: [1, 0]
      }, options)
    } 
}

function render(source){
  const $ = document.createElement('div')

  $.innerHTML = `
    <div style="
      transform-origin: 50% 50%;
      position: fixed;
      height: 100vh;
      width: 100vw;
      left: 0; 
      top: 0;
    ">
      <object 
        type=image/svg+xml 
        data="data:image/svg+xml;base64,${ btoa(source) }"
        style="object-fit: contain">
      </object>
    </div>
  `
  
  return document.body.appendChild(
    $.firstElementChild
  )
}

const arrow = `\
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 640 640">
  <defs/>
  <defs>
    <path id="a" d="M311 0L0 320l311 320V437h329V202H311V0z"/>
  </defs>
  <use fill="#492d67" xlink:href="#a"/>
</svg>
`

const circle = `\
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 640 640">
  <defs/>
  <defs>
    <path id="a" d="M640 320a320 320 0 11-640 0 320 320 0 01640 0z"/>
  </defs>
  <use fill="#f22ce6" xlink:href="#a"/>
</svg>
`

const x = `\
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 640 640">
  <defs/>
  <defs>
    <path id="a" d="M435 320l205 205-115 115-205-205-205 205L0 525l205-205L0 115 115 0l205 205L525 0l115 115-205 205z"/>
  </defs>
  <use fill="#492d67" xlink:href="#a"/>
</svg>
`

manifest.json

{

  "manifest_version": 2,
  "name": "Traverse",
  "version": "1.0",

  "description": "Forum navigation assistance script. Finds common previous / next page link patterns and binds their actions to Ctrl + ⟵ / Ctrl + ⟶ keyboard commands.",

  "icons": {
    "64": "icons/traverse.svg"
  },

  "content_scripts": [
    {
      "matches": ["<all_urls>"],
      "js": ["DOM.js"],
      "run_at": "document_end"
    }
  ],

  "commands": {
    "previous": {
      "suggested_key": {
        "default": "Ctrl+Left",
        "mac": "MacCtrl+Left"
      },

      "description": "Navigate to previous page in thread"
    },

    "next": {
      "suggested_key": {
        "default": "Ctrl+Right",
        "mac": "MacCtrl+Right"
      },

      "description": "Navigate to next page in thread"
    }
  }
}

traverse.js

// Commands interface
browser.commands.onCommand.addListener(direction =>
  act(controls[direction])
)

// Controls are searched for on request...
const controls = new Proxy({}, {
  get: (_, command) => _[command] || findControls()[command]
})

// ...up until the document is ready, at which point they're fixed
document.addEventListener('DOMContentLoaded', () => {
  Object.assign(controls, findControls())
})
 
// Text patterns used by pagination controls, 
// in order of most to least likely / ambiguous
const patterns = [
  ['previous', 'next'],
  ['<',        '>'   ],
  ['prev',     'next'],
  ['‹',        '›'   ],
  ['«',        '»'   ],
  ['<<',       '>>'  ],
].map(pair => 
  pair.map(string => 
    new RegExp('\\s*' + string + '\\s*', 'i')
  )
)

// Element properties to test those patterns on
const properties = ['textContent', 'rel', 'title']

function findControls() {
  const controls = {}
  const $all = Array.from(document.all)
  
  // The 2 commands, whose index maps to that of the pattern pair (0 , 1)
  void ['previous', 'next'].forEach((command, index) =>
    // Iterate through the patterns
    patterns.find(pair =>
      // And for every element on the page
      $all.find($ =>
        // If any of the relevant element properties match the pattern... 
        properties.some(property =>
          pair[index].test($[property])
        )

        &&
        
        // The containing actionable element is the pertinent control
        (controls[command] = $.closest('a,button,input'))
      )
    )
  )

  return controls
}

// Activate pagination controls
function act($) {
  if ($.onclick)
    $.onclick()

  if ($.matches('a'))
    window.location.assign($.href)

  else if ($.matches('input[type=submit]'))
    $.form.submit()
}

traverse.svg