Cache webpack to use on subsequent compiles

index.js

@@ -23,7 +23,16 @@ var defaultStatsOptions = {
   errorDetails: false
 };
 
+var cache = {};
+
 module.exports = function (options, wp, done) {
+  if (cache.wp !== wp || cache.options !== options) {
+    cache = {};
+  }
+
+  cache.options = options;
+  cache.wp = wp;
+
   options = clone(options) || {};
   if (typeof done !== 'function') {
     var callingDone = false;
@@ -103,7 +112,11 @@ module.exports = function (options, wp, done) {
       return self.emit('end');
     }
 
-    var compiler = webpack(options, function (err, stats) {
+    // Cache compiler for future use
+    var compiler = cache.compiler || webpack(options);
+    cache.compiler = compiler;
+
+    compiler.run(function (err, stats) {
       if (err) {
         self.emit('error', new gutil.PluginError('webpack-stream', err));
       }
@@ -140,7 +153,9 @@ module.exports = function (options, wp, done) {
       }));
     }
 
-    var fs = compiler.outputFileSystem = new MemoryFileSystem();
+    cache.mfs = cache.mfs || new MemoryFileSystem();
+
+    var fs = compiler.outputFileSystem = cache.mfs;
 
     compiler.plugin('after-emit', function (compilation, callback) {
       Object.keys(compilation.assets).forEach(function (outname) {

test/test.js

@@ -59,6 +59,51 @@ test('multiple entry points', function (t) {
   stream.end();
 });
 
+test('subsequent runs served from cache', function (t) {
+  t.plan(4);
+
+  var config = {
+    entry: {
+      'one': path.join(base, 'entry.js'),
+      'two': path.join(base, 'anotherentrypoint.js')
+    },
+    output: {
+      filename: '[name].bundle.js'
+    },
+    quiet: true
+  };
+
+  var stream = webpack(config);
+  stream.on('data', function (file) {
+    var basename = path.basename(file.path);
+    var contents = file.contents.toString();
+    switch (basename) {
+      case 'one.bundle.js':
+        t.ok(/__webpack_require__/i.test(contents), 'should contain "__webpack_require__"');
+        t.ok(/var one = true;/i.test(contents), 'should contain "var one = true;"');
+        break;
+      case 'two.bundle.js':
+        t.ok(/var anotherentrypoint = true;/i.test(contents), 'should contain "var anotherentrypoint = true;"');
+        break;
+    }
+  });
+
+  stream.on('end', function () {
+    var cachedStream = webpack(config);
+    var data = null;
+
+    cachedStream.on('data', function (file) {
+      data = file;
+    });
+
+    cachedStream.on('end', function () {
+      t.ok(data === null, 'should not write any output');
+    });
+  });
+
+  stream.end();
+});
+
 test('stream multiple entry points', function (t) {
   t.plan(3);
   var entries = fs.src(['test/fixtures/entry.js', 'test/fixtures/anotherentrypoint.js']);