Added a file with common prototype extensions I use.

prototype_extensions.js

@@ -0,0 +1,63 @@
+Object.extend(String.prototype, {
+  // if a string doesn't end with str it appends it
+  ensureEndsWith: function(str) {
+    return this.endsWith(str) ? this : this + str;
+  },
+
+  // makes sure that string ends with px (for setting widths and heights)
+  px: function() {
+    return this.ensureEndsWith('px');
+  }
+});
+
+Object.extend(Number.prototype, {
+  // makes sure that number ends with px (for setting widths and heights)
+  px: function() {
+    return this.toString().px();
+  }
+});
+
+var Window = {
+  // returns correct dimensions for window, had issues with prototype's sometimes. this was ganked from apple.
+  size: function() {
+		var width  = window.innerWidth || (window.document.documentElement.clientWidth || window.document.body.clientWidth);
+		var height = window.innerHeight || (window.document.documentElement.clientHeight || window.document.body.clientHeight);
+		var x      = window.pageXOffset || (window.document.documentElement.scrollLeft || window.document.body.scrollLeft);
+		var y      = window.pageYOffset || (window.document.documentElement.scrollTop || window.document.body.scrollTop);
+		return {'width':width, 'height':height, 'x':x, 'y':y}
+	}
+}
+
+// some goodies for converting numbers and strings to currency format
+Object.extend(String.prototype, {
+	toFloat: function() {
+		f = parseFloat(this.gsub(/[^0-9\.]/, ''));
+		return (isNaN(f)) ? 0.0 : f;
+	},
+
+	/* only supports . as separator because of parseFloat use */
+	toCurrency: function(o) {
+		var dollars = 0, cents = 0;
+		var options = $H({ precision:2, unit:'$' }).merge(o)
+		var amount  = new String(this).gsub(/[^0-9\.]/, '');
+		var parts   = amount.split('.');
+
+		if (parts.length > 1) {
+			dollars = parts[0];
+			cents = parts[1];
+		} else {
+			dollars = parseInt(parts[0]);
+			cents = 0;
+		}
+
+		if (isNaN(parseInt(dollars))) { dollars = 0; }
+		if (isNaN(parseInt(cents))) 	{ cents = 0; }
+		return options.get('unit') + parseFloat(dollars + '.' + cents).toFixed(options.get('precision'));
+	}
+});
+
+Object.extend(Number.prototype, {
+	toCurrency: function() {
+		return new String(this).toCurrency();
+	}
+});