Working chrome extension

currency_munger.js

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+var currencyRegExp = new RegExp('(\u00A3|\\$)(\\d[\\d,\.]*)\\s?((bn)|(billion)|(m)|(million)|(k)|(thousand)|(trillion)|(tn))?');
+
+var conversion_factors = {
+	"teachers" : { "text": "the cost of employing [[number]] new teachers", "factor": 20427 },
+	"schools" : {"text": "the cost of building [[number]] new schools", "factor": 25000000},
+	"per uk person" : {"text": "£[[number]] for every man, woman and child in the UK", "factor": 66000000},
+	"afghanistan": {"text": "[[number]]% of the uk operational cost of the Afghanistan war", "factor": 7440000},
+	"wispa": {"text": "the cost of [[number]] Wispas", "factor": 0.80},
+	"pound years": {"text": "£1 every second for [[number]] years", "factor": 31556926 },
+	"tonnes of pennies": {"text": "[[number]] tonnes of pennies", "factor": 2857},
+	"ross years": {"text": "[[number]] years of Jonathan Ross's salary", "factor": 6000000},
+	"ten pound notes": {"text": "[[number]]% of ten pound notes in circulation", "factor": 560000000}
+};
+
+var currency_munger = {
+
+	remove_previous: function() {
+		var equivalents = document.evaluate("//span[@class='money_equivalent']", document.body,
+							   null, XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE, null);
+		for (var i = 0; i < equivalents.snapshotLength; i++) {
+			var equivalent = equivalents.snapshotItem(i);
+			equivalent.parentNode.removeChild(equivalent);
+		};
+	},
+
+	human_readable: function(number) {
+		var suffix = '';
+		if (number > Math.pow(10,12)) {
+			suffix = ' trillion';
+			number = number / Math.pow(10,12);
+		};
+		if (number > Math.pow(10,9)) {
+			suffix = ' billion';
+			number = number / Math.pow(10,9);
+		};
+		if (number > Math.pow(10,6)) {
+			suffix = ' million';
+			number = number / Math.pow(10,6);
+		};
+		number = Math.round(number*100)/100 // two decimal digits
+	    number += ''; // must be a better way to convert to a string?
+	    parts = number.split('.');
+	    whole_num = parts[0];
+	    decimal = parts.length > 1 ? '.' + parts[1] : '';
+	    var regexp = /(\d+)(\d{3})/;
+	    while (regexp.test(whole_num))
+	        whole_num = whole_num.replace(regexp, '$1' + ',' + '$2');
+	    return  whole_num + decimal + suffix;
+	},
+
+	munge: function(matches,requested_scale,article) {
+		amount = parseFloat(matches[2].replace(/,/g,''));
+
+		if (matches[1] == '$') {
+			amount = amount * 0.68 // dollar pound exchange rate
+		}
+
+		switch (matches[3]) {
+			case 'trillion': 
+			case 'tn':
+				amount = amount * Math.pow(10,12); break;
+
+			case 'billion':
+			case 'bn': amount = amount * Math.pow(10,9); break;
+
+			case 'million':
+			case 'm': amount = amount * Math.pow(10,6); break;
+
+			case 'thousand':
+			case 'k': amount = amount * Math.pow(10,3); break;
+		}
+
+		var scale = conversion_factors[requested_scale]
+		var factor = scale["factor"];
+		var number = Math.round(amount / factor);
+		var text = scale["text"].replace('[[number]]',currency_munger.human_readable(number));
+		if (number > 0) {
+			var equivalent = " ("+text+") ";
+			var insert = document.createElement('span');
+			insert.className = "money_equivalent";
+			insert.appendChild(document.createTextNode(equivalent));
+			article.parentNode.insertBefore(insert,article);
+		}
+	},
+
+	replace_numbers: function(requested_scale) {
+		currency_munger.remove_previous();
+		var articleDivX = document.evaluate("//text()[ancestor::div]", document.body,
+							   null, XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE, null);
+		for (var i = 0; i < articleDivX.snapshotLength; i++) {
+			var article = articleDivX.snapshotItem(i);
+			var articleText = article.nodeValue;
+			var matches = currencyRegExp.exec(articleText);
+			while (matches) {
+				var searchIndex = matches.index;
+				article.splitText(searchIndex + matches[0].length);
+				article = article.nextSibling;
+
+				currency_munger.munge(matches,requested_scale,article);
+
+				articleText = article.nodeValue; 
+				matches = currencyRegExp.exec(articleText);
+			}
+		}
+	}
+};
+
+function processRequest(request, sender, sendResponse) {
+		switch(request.command)
+		{
+			case("getSettings"):
+				sendResponse(conversion_factors);
+				return;
+			case("highlight"):
+			  currency_munger.replace_numbers(request.value);
+			  break;
+			case("clear"):
+			  currency_munger.remove_previous();
+			  break;
+		}
+
+		sendResponse({});		
+
+}
+
+chrome.extension.onRequest.addListener(processRequest);

manifest.json

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+{
+  "name": "Currency Munger",
+  "version": "1.0",
+  "description": "Make currency amounts a bit more understandable",
+  "browser_action": {
+    "default_icon": "icon.png",
+    "popup": "popup.html"
+  },
+  "permissions": [ "tabs", "http://*/*"],
+  "content_scripts": 	
+  	[{
+  	    "matches": ["http://*/*"],
+  		"js": [ "currency_munger.js" ]
+  	}]
+} 

popup.html

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+<style>
+body {
+  min-width:357px;
+  overflow-x:hidden;
+}
+</style>
+
+<script>
+  var conversion_factors = {};
+  var styles_inserted = false;
+
+  var sendToCurrentTab = function(command,callback) {
+    chrome.tabs.getSelected(null, function(tab) {
+      chrome.tabs.sendRequest(tab.id,command,callback);
+    });
+  }
+
+  var highlight = function(v) {
+    if (!styles_inserted) {
+      addGlobalStyles('.money_equivalent { color: #990000 ! important; font-weight: bold;}');
+      styles_inserted = true;
+    }
+    sendToCurrentTab({command:'highlight',value:v});
+  }
+
+  var unhighlight = function() {
+    sendToCurrentTab({command:'clear'});
+  }
+
+  var addGlobalStyles = function(css) {
+    chrome.tabs.getSelected(null, function(tab) {
+	    chrome.tabs.insertCSS(tab.id,{code:css});
+	  });
+	}
+
+  var create_menu = function() {	
+	  var menu = '';
+	  for (var i in conversion_factors) {
+	    menu += '<li><a href="#" onclick="highlight(\''+i+'\')">' + i + '</a></li>';
+	  };
+	  menu += '<li><a href="#" onclick="unhighlight()">[x] clear all</a></li>';
+
+	  var header = document.createElement('h1');
+	  header.innerHTML = "Is it worth it?"
+
+	  var menuobj = document.createElement('ul');
+	  menuobj.className = "money_menu"
+	  menuobj.innerHTML = menu;
+	  var body = document.getElementsByTagName('body')[0];
+	  body.appendChild(header);
+	  body.appendChild(menuobj);
+	};
+
+	var init = function(data) {
+	   conversion_factors = data;
+	   create_menu();
+	};
+
+	sendToCurrentTab({command:"getSettings"}, init);
+
+</script>
+<body>
+
+</body>