Add cache option to 6to5-node

lib/6to5/register.js

@@ -1,8 +1,10 @@
 require("./polyfill");
 
 var sourceMapSupport = require("source-map-support");
+var roadrunner       = require('roadrunner');
 var util             = require("./util");
 var to5              = require("./index");
+var fs               = require("fs");
 var _                = require("lodash");
 
 sourceMapSupport.install({
@@ -61,22 +63,38 @@ var transformOpts = {};
 var ignoreRegex   = /node_modules/;
 var onlyRegex;
 var whitelist     = [];
+var cache;
 var exts          = {};
 var maps          = {};
 var old           = require.extensions[".js"];
 
+var mtime = function (filename) {
+  return +fs.statSync(filename).mtime;
+};
+
 var loader = function (m, filename) {
   if ((ignoreRegex && ignoreRegex.test(filename)) || (onlyRegex && !onlyRegex.test(filename))) {
     return old.apply(this, arguments);
   }
 
-  var result = to5.transformFileSync(filename, _.extend({
+  var result;
+
+  if (cache && cache[filename].mtime === mtime(filename)) {
+    result = cache[filename];
+  }
+
+  result = result || to5.transformFileSync(filename, _.extend({
     whitelist: whitelist,
     blacklist: blacklist,
     sourceMap: true,
     modules:   "commonInterop"
   }, transformOpts));
 
+  if (cache) {
+    result.mtime = mtime(filename);
+    cache[filename] = result;
+  }
+
   maps[filename] = result.map;
 
   m._compile(result.code, filename);
@@ -108,5 +126,8 @@ module.exports = function (opts) {
 
   if (opts.extensions) hookExtensions(util.arrayify(opts.extensions));
 
+  if (opts.cache) cache = roadrunner.get('6to5');
+  if (opts.cache === false) cache = null;
+
   _.extend(transformOpts, opts);
 };