content_script.js

//Global variables
var destinations = {}
var targets = {}
var links = []
var timer

// List of domains this extension should be disabled on
var ignoredDomains = [
	/docs\.google\.com/
]

// Resets the timer and causes populateDestinations() to be called after a delay
function resetDestinations(){
	destinations = {}
	if(timer){
		clearTimeout(timer)
	}
	timer = setTimeout(populateDestinations, 50)
}

// Populates the list of destinations
function populateDestinations(){

	// Reset the timer
	if(timer){
		clearTimeout(timer)
	}
	timer = null

	// Reset the list of destinations
	destinations = {
		prev: null,
		next: null,
		up: null,
		top: null
	}
	targets = {
		prev: null,
		next: null,
		up: null,
		top: null
	}

	// Search through elements in document order
	links = [].concat(
		Array.prototype.slice.call(document.getElementsByTagName("LINK")),
		Array.prototype.slice.call(document.getElementsByTagName("A"))
	)

	// Determine the destinations of the rels we care about
	for(var i in links){
		if(!links[i].rel || !links[i].href) continue
		for(var dest in destinations){
			if(links[i].rel.toLowerCase() == dest){
				destinations[dest] = links[i].href
				if(links[i].tagName == "A") targets[dest] = links[i]
			}
		}
	}

	// Flip the links to now search bottom-up
	links = links.reverse()

	// Search for destinations based on link contents
	for(var dest in destinations){

		// Skip destinations that have already been matched to an A-link
		if(destinations[dest] && targets[dest]) continue

		// Track an expression matching array
		var regexes = []

		if(dest == "next"){
			regexes.push(/\bnext\b/i)

			// de
			regexes.push(/\bnächste seite\b/i)
			regexes.push(/\bnächste\b/i)
			regexes.push(/\bnächstes\b/i)
			regexes.push(/\bweiter\b/i)

			// ru (\b does not support unicode though regexp does)
			regexes.push(/вперёд/i)
			regexes.push(/следующий/i)
			regexes.push(/следующая/i)
			regexes.push(/след/i)
			regexes.push(/позже/i)

			// ua
			regexes.push(/вперед/i)
			regexes.push(/наступна/i)
			regexes.push(/пізніше/i)

			regexes.push(/→/i)
			regexes.push(/»/i)

			// i.mdi-navigation-chevron-right
		}
		if(dest == "prev"){
			regexes.push(/\bprev(ious)?\b/i)

			// de
			regexes.push(/\bvorherige seite\b/i)
			regexes.push(/\bvorherige\b/i)
			regexes.push(/\bzurück\b/i)

			// ru
			regexes.push(/назад/i)
			regexes.push(/предыдущий/i)
			regexes.push(/предыдущая/i)
			regexes.push(/пред/i)
			regexes.push(/раньше/i)

			// ua
			regexes.push(/назад/i)
			regexes.push(/попередня/i)
			regexes.push(/раніше/i)

			regexes.push(/←/i)
			regexes.push(/«/i)
		}
		if(dest == "up"){
			regexes.push(/\bup\b/i)
		}
		if(dest == "top"){
			regexes.push(/\bhome\b/i)
		}

		// Attempt to match links based on text or class name (first match wins)
		(function(){
			for(var r in regexes){
				for(var i in links){
					var text = links[i].innerText.trim()
					var className = links[i].className.trim()
					if(
						links[i].href
						&& (text.match(regexes[r]) || className.match(regexes[r]))
					){
						destinations[dest] = links[i].href
						targets[dest] = links[i]
						return	// Breaks 2 loops
					}
				}
			}
		})()

	}

}

// Keyboard event handler
function keyListener(e){

	// Assume windows settings by default
	var cmdKey = e.ctrlKey
	var ignoreKey = e.altKey

	// Detect the shortcut sequence based on OS
	if(navigator.platform.match(/^Mac/)){
		cmdKey = e.altKey
		ignoreKey = e.ctrlKey
	}

	// Ignore anything with ignored key in it
	if(e.ignoreKey) return

	// Repopulate if we don't yet exist
	if(!destinations) populateDestinations()

	var action = null

	// Key + Left
	if(cmdKey && !e.shiftKey && e.keyCode == 37 && destinations.prev){
		action = "prev"
	}

	// Key + Right
	if(cmdKey && !e.shiftKey && e.keyCode == 39 && destinations.next){
		action = "next"
	}

	// Key + Up
	if(cmdKey && !e.shiftKey && e.keyCode == 38 && destinations.up){
		action = "up"
	}

	// Key + Shift + Up
	if(cmdKey && e.shiftKey && e.keyCode == 38 && destinations.top){
		action = "top"
	}

	// Space (when scrolled to the bottom of the window)
	if(!cmdKey && !e.shiftKey && e.keyCode == 32 && e.srcElement == document.body && destinations.next){
		if(document.body.scrollHeight - document.body.scrollTop - document.documentElement.clientHeight <= 0){
			action = "next"
		}
	}

	// Shift + Space (when scrolled to the top of the window)
	if(!cmdKey && e.shiftKey && e.keyCode == 32 && e.srcElement == document.body && destinations.prev){
		if(!document.body.scrollTop) action = "prev"
	}

	if(!action || e.srcElement.tagName == "INPUT" || e.srcElement.tagName == "TEXTAREA") return

	// Cancel the event's default action
	e.preventDefault()

	// Navigate or click the link
	if(targets[action]){
		targets[action].click()
	}else{
		window.location = destinations[action]
	}

}

// The key listening event should only be bound to the top window
if (window == top) {

	// Check the ignored domain list
	var bindEvents = true
	for (var i = 0; i < ignoredDomains.length; i++){
		if(window.location.hostname.match(ignoredDomains[i])){
			bindEvents = false
			break
		}
	}

	// Bind the key handlers
	if(bindEvents){
		document.addEventListener('DOMSubtreeModified', resetDestinations)
		window.addEventListener('keydown', keyListener, false)
	}

}

// Initial population
resetDestinations()