diff --git a/js/utils.js b/js/utils.js
new file mode 100644
index 00000000..6bb4ae7a
--- /dev/null
+++ b/js/utils.js
@@ -0,0 +1,137 @@
+// YYY Should probably have two versions: node vs browser
+
+var fs = require("fs");
+var path = require("path");
+
+Function.prototype.method = function(name,func) {
+	this.prototype[name] = func;
+
+	return this;
+};
+
+var filterErr = function(code, done) {
+    return function(e) {
+			done(e.code !== code ? e : undefined);
+		};
+};
+
+var throwErr = function(done) {
+    return function(e) {
+			if (e)
+				throw e;
+			
+			done();
+		};
+};
+ 
+// apply function to elements of array. Return first true value to done or undefined.
+var mapOr = function(func, array, done) {
+    if (array.length) {
+		func(array[array.length-1], function(v) {
+				if (v) {
+					done(v);
+				}
+				else {
+					array.length -= 1;
+					mapOr(func, array, done);
+				}
+			});
+    }
+    else {
+		done();
+    }
+};
+
+// Make a directory and sub-directories.
+var mkPath = function(dirPath, mode, done) {
+    fs.mkdir(dirPath, typeof mode === "string" ? parseInt(mode, 8) : mode, function(e) {
+		if (!e ||  e.code === "EEXIST") {
+			// Created or already exists, done.
+			done();
+	    }
+	    else if (e.code === "ENOENT") {
+			// Missing sub dir.
+
+			mkPath(path.dirname(dirPath), mode, function(e) {
+					if (e) {
+						throw e;
+					}
+					else {
+						mkPath(dirPath, mode, done);
+					}
+				});
+	    }
+	    else {
+			throw e;
+	    }
+	});
+};
+
+// Empty a directory.
+var emptyPath = function(dirPath, done) {
+    fs.readdir(dirPath, function(err, files) {
+	if (err) {
+	    done(err);
+	}
+	else {
+	    mapOr(rmPath, files.map(function(f) { return path.join(dirPath, f); }), done);
+	}
+    });
+};
+
+// Remove path recursively.
+var rmPath = function(dirPath, done) {
+//  console.log("rmPath: %s", dirPath);
+
+    fs.lstat(dirPath, function(err, stats) {
+			if (err && err.code == "ENOENT") {
+				done();
+			}
+			if (err) {
+				done(err);
+			}
+			else if (stats.isDirectory()) {
+				emptyPath(dirPath, function(e) {
+						if (e) {
+							done(e);
+						}
+						else {
+//							console.log("rmdir: %s", dirPath); done();
+							fs.rmdir(dirPath, done);
+						}
+					});
+			}
+			else {
+//				console.log("unlink: %s", dirPath); done();
+				fs.unlink(dirPath, done);
+			}
+		});
+};
+
+// Create directory if needed and empty if needed.
+var resetPath = function(dirPath, mode, done) {
+    mkPath(dirPath, mode, function(e) {
+			if (e) {
+				done(e);
+			}
+			else {
+				emptyPath(dirPath, done);
+			}
+		});
+};
+
+var trace = function(comment, func) {
+    return function() {
+			console.log("%s: %s", trace, arguments.toString);
+			func(arguments);
+		};
+};
+
+exports.emptyPath   = emptyPath;
+exports.mapOr	    = mapOr;
+exports.mkPath	    = mkPath;
+exports.resetPath   = resetPath;
+exports.rmPath	    = rmPath;
+exports.trace	    = trace;
+
+// vim:ts=4