from /honestbleeps/RedditEnhancementSuite -- the filteReddit "filter by keyword" functoinality

res-filter-keyword

  filterTitle: function(title, reddit) {
		var reddit = (reddit) ? reddit.toLowerCase() : null;
		return this.arrayContainsSubstring(this.options.keywords.value, title.toLowerCase(), reddit);
	},
	filterDomain: function(domain, reddit) {
		var reddit = (reddit) ? reddit.toLowerCase() : null;
		var domain = (domain) ? domain.toLowerCase() : null;
		return this.arrayContainsSubstring(this.options.domains.value, domain, reddit);
	},
	filterSubreddit: function(subreddit) {
		return this.arrayContainsSubstring(this.options.subreddits.value, subreddit.toLowerCase(), null, true);
	},
	filterFlair: function(flair, reddit) {
		var reddit = (reddit) ? reddit.toLowerCase() : null;
		return this.arrayContainsSubstring(this.options.flair.value, flair.toLowerCase(), reddit);
	},
	unescapeHTML: function(theString) {
		var temp = document.createElement("div");
		$(temp).html(theString);
		var result = temp.childNodes[0].nodeValue;
		temp.removeChild(temp.firstChild);
		delete temp;
		return result;	
	},
	arrayContainsSubstring: function(obj, stringToSearch, reddit, fullmatch) {
		stringToSearch = this.unescapeHTML(stringToSearch);
		var i = obj.length;
		while (i--) {
			if ((typeof(obj[i]) != 'object') || (obj[i].length<3)) {
				if (obj[i].length == 1) obj[i] = obj[i][0];
				obj[i] = [obj[i], 'everywhere',''];
			}
			var searchString = obj[i][0];
			var applyTo = obj[i][1];
			var applyList = obj[i][2].toLowerCase().split(',');
			var skipCheck = false;
			switch (applyTo) {
				case 'exclude':
					if (applyList.indexOf(reddit) != -1) {
						skipCheck = true;
					}
					break;
				case 'include':
					if (applyList.indexOf(reddit) == -1) {
						skipCheck = true;
					}
					break;
			}
			// if fullmatch is defined, don't do a substring match... this is used for subreddit matching on /r/all for example
			if ((!skipCheck) && (fullmatch) && (obj[i] != null) && (stringToSearch.toLowerCase() == searchString.toLowerCase())) return true;
			if ((!skipCheck) && (!fullmatch) && (obj[i] != null) && (stringToSearch.indexOf(searchString.toString().toLowerCase()) != -1)) {
				return true;
			}
		}
		return false;
	},