diff --git a/README.md b/README.md
index a17eea8..6d48ccd 100644
--- a/README.md
+++ b/README.md
@@ -15,6 +15,24 @@ However, you should use it directly when developing bindings for external build
 
 Supports any options from [escodegen documentation](https://github.com/Constellation/escodegen/wiki/API).
 
+### option.generator
+
+Allow passing a custom Obserable generator, either directly or as a factory function.
+
+The `defaultGenerator` used if no `generator` option passed:
+
+```js
+function defaultGenerator(options) {
+    return function(files) {
+        return files.flatMap(function (file) {
+            var result = escodegen.generate(file.program, options);
+            // ...
+            return Rx.Observable.fromArray(files);
+        })
+    }
+}
+```
+
 ## License
 
 [MIT License](http://en.wikipedia.org/wiki/MIT_License)
diff --git a/index.js b/index.js
index cb108f9..b8ffda3 100644
--- a/index.js
+++ b/index.js
@@ -3,14 +3,8 @@
 var Rx = require('rx');
 var escodegen = require('escodegen');
 
-module.exports = function (options) {
-	options = options || {};
-	if (typeof options.format === 'string') {
-		options.format = escodegen[options.format];
-	}
-	options.sourceMapWithCode = true;
-
-	return function (files) {
+function defaultGenerator(options) {
+	return function(files) {
 		return files.flatMap(function (file) {
 			var result = escodegen.generate(file.program, options);
 
@@ -38,6 +32,17 @@ module.exports = function (options) {
 			}
 
 			return Rx.Observable.fromArray(files);
-		});
-	};
+		})
+	}
+};
+
+module.exports = function (options) {
+	options = options || {};
+	if (typeof options.format === 'string') {
+		options.format = escodegen[options.format];
+	}
+	options.sourceMapWithCode = true;
+
+	let generator = options.generator || defaultGenerator
+	return typeof generator === 'function' ? generator(options) : generator
 };
diff --git a/package.json b/package.json
index 5fe0952..892f046 100644
--- a/package.json
+++ b/package.json
@@ -16,12 +16,13 @@
     "test": "mocha"
   },
   "dependencies": {
-    "escodegen": "^1.4.1",
-    "rx": "^2.3.11"
+    "escodegen": "^1.8.1",
+    "esprima": "^3.1.1",
+    "rx": "^4.1.0"
   },
   "devDependencies": {
     "chai": "*",
-    "esprima": "^1.2.2",
+    "esprima": "^3.1.1",
     "mocha": "*"
   }
 }
diff --git a/test/test.js b/test/test.js
index 996cf9d..ac7588c 100644
--- a/test/test.js
+++ b/test/test.js
@@ -4,7 +4,8 @@
 
 var assert = require('chai').assert,
 	Rx = require('rx'),
-	parse = require('esprima').parse,
+	esprima = require('esprima'),
+	parse = esprima.parse,
 	generate = require('..');
 
 it('test', function (done) {
@@ -26,10 +27,15 @@ it('test', function (done) {
 			}
 		];
 
+	var index = 0;
 	// simulating file sequence and applying transformation
 	generate({comment: true, sourceMap: true})(Rx.Observable.fromArray(input))
 	// checking against array of expected results iteratively
-	.zip(expected, assert.deepEqual)
+	.do(function (file) {
+		assert.deepEqual(file, expected[index++]);
+	})
+
+	// .zip(expected, assert.deepEqual)
 	// subscribing to check results
 	.subscribe(function () {}, done, done);
 });
diff --git a/yarn.lock b/yarn.lock
new file mode 100644
index 0000000..21ab1b5
--- /dev/null
+++ b/yarn.lock
@@ -0,0 +1,293 @@
+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+amdefine@>=0.0.4:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/amdefine/-/amdefine-1.0.1.tgz#4a5282ac164729e93619bcfd3ad151f817ce91f5"
+
+assertion-error@^1.0.1:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/assertion-error/-/assertion-error-1.0.2.tgz#13ca515d86206da0bac66e834dd397d87581094c"
+
+balanced-match@^0.4.1:
+  version "0.4.2"
+  resolved "https://registry.yarnpkg.com/balanced-match/-/balanced-match-0.4.2.tgz#cb3f3e3c732dc0f01ee70b403f302e61d7709838"
+
+brace-expansion@^1.0.0:
+  version "1.1.6"
+  resolved "https://registry.yarnpkg.com/brace-expansion/-/brace-expansion-1.1.6.tgz#7197d7eaa9b87e648390ea61fc66c84427420df9"
+  dependencies:
+    balanced-match "^0.4.1"
+    concat-map "0.0.1"
+
+browser-stdout@1.3.0:
+  version "1.3.0"
+  resolved "https://registry.yarnpkg.com/browser-stdout/-/browser-stdout-1.3.0.tgz#f351d32969d32fa5d7a5567154263d928ae3bd1f"
+
+chai@*:
+  version "3.5.0"
+  resolved "https://registry.yarnpkg.com/chai/-/chai-3.5.0.tgz#4d02637b067fe958bdbfdd3a40ec56fef7373247"
+  dependencies:
+    assertion-error "^1.0.1"
+    deep-eql "^0.1.3"
+    type-detect "^1.0.0"
+
+commander@2.9.0:
+  version "2.9.0"
+  resolved "https://registry.yarnpkg.com/commander/-/commander-2.9.0.tgz#9c99094176e12240cb22d6c5146098400fe0f7d4"
+  dependencies:
+    graceful-readlink ">= 1.0.0"
+
+concat-map@0.0.1:
+  version "0.0.1"
+  resolved "https://registry.yarnpkg.com/concat-map/-/concat-map-0.0.1.tgz#d8a96bd77fd68df7793a73036a3ba0d5405d477b"
+
+debug@2.2.0:
+  version "2.2.0"
+  resolved "https://registry.yarnpkg.com/debug/-/debug-2.2.0.tgz#f87057e995b1a1f6ae6a4960664137bc56f039da"
+  dependencies:
+    ms "0.7.1"
+
+deep-eql@^0.1.3:
+  version "0.1.3"
+  resolved "https://registry.yarnpkg.com/deep-eql/-/deep-eql-0.1.3.tgz#ef558acab8de25206cd713906d74e56930eb69f2"
+  dependencies:
+    type-detect "0.1.1"
+
+deep-is@~0.1.3:
+  version "0.1.3"
+  resolved "https://registry.yarnpkg.com/deep-is/-/deep-is-0.1.3.tgz#b369d6fb5dbc13eecf524f91b070feedc357cf34"
+
+diff@1.4.0:
+  version "1.4.0"
+  resolved "https://registry.yarnpkg.com/diff/-/diff-1.4.0.tgz#7f28d2eb9ee7b15a97efd89ce63dcfdaa3ccbabf"
+
+escape-string-regexp@1.0.5:
+  version "1.0.5"
+  resolved "https://registry.yarnpkg.com/escape-string-regexp/-/escape-string-regexp-1.0.5.tgz#1b61c0562190a8dff6ae3bb2cf0200ca130b86d4"
+
+escodegen@^1.8.1:
+  version "1.8.1"
+  resolved "https://registry.yarnpkg.com/escodegen/-/escodegen-1.8.1.tgz#5a5b53af4693110bebb0867aa3430dd3b70a1018"
+  dependencies:
+    esprima "^2.7.1"
+    estraverse "^1.9.1"
+    esutils "^2.0.2"
+    optionator "^0.8.1"
+  optionalDependencies:
+    source-map "~0.2.0"
+
+esprima:
+  version "3.1.1"
+  resolved "https://registry.yarnpkg.com/esprima/-/esprima-3.1.1.tgz#02dbcc5ac3ece81070377f99158ec742ab5dda06"
+
+esprima@^2.7.1:
+  version "2.7.3"
+  resolved "https://registry.yarnpkg.com/esprima/-/esprima-2.7.3.tgz#96e3b70d5779f6ad49cd032673d1c312767ba581"
+
+estraverse@^1.9.1:
+  version "1.9.3"
+  resolved "https://registry.yarnpkg.com/estraverse/-/estraverse-1.9.3.tgz#af67f2dc922582415950926091a4005d29c9bb44"
+
+esutils@^2.0.2:
+  version "2.0.2"
+  resolved "https://registry.yarnpkg.com/esutils/-/esutils-2.0.2.tgz#0abf4f1caa5bcb1f7a9d8acc6dea4faaa04bac9b"
+
+fast-levenshtein@~2.0.4:
+  version "2.0.5"
+  resolved "https://registry.yarnpkg.com/fast-levenshtein/-/fast-levenshtein-2.0.5.tgz#bd33145744519ab1c36c3ee9f31f08e9079b67f2"
+
+fs.realpath@^1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/fs.realpath/-/fs.realpath-1.0.0.tgz#1504ad2523158caa40db4a2787cb01411994ea4f"
+
+glob@7.0.5:
+  version "7.0.5"
+  resolved "https://registry.yarnpkg.com/glob/-/glob-7.0.5.tgz#b4202a69099bbb4d292a7c1b95b6682b67ebdc95"
+  dependencies:
+    fs.realpath "^1.0.0"
+    inflight "^1.0.4"
+    inherits "2"
+    minimatch "^3.0.2"
+    once "^1.3.0"
+    path-is-absolute "^1.0.0"
+
+"graceful-readlink@>= 1.0.0":
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/graceful-readlink/-/graceful-readlink-1.0.1.tgz#4cafad76bc62f02fa039b2f94e9a3dd3a391a725"
+
+growl@1.9.2:
+  version "1.9.2"
+  resolved "https://registry.yarnpkg.com/growl/-/growl-1.9.2.tgz#0ea7743715db8d8de2c5ede1775e1b45ac85c02f"
+
+has-flag@^1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/has-flag/-/has-flag-1.0.0.tgz#9d9e793165ce017a00f00418c43f942a7b1d11fa"
+
+inflight@^1.0.4:
+  version "1.0.6"
+  resolved "https://registry.yarnpkg.com/inflight/-/inflight-1.0.6.tgz#49bd6331d7d02d0c09bc910a1075ba8165b56df9"
+  dependencies:
+    once "^1.3.0"
+    wrappy "1"
+
+inherits@2:
+  version "2.0.3"
+  resolved "https://registry.yarnpkg.com/inherits/-/inherits-2.0.3.tgz#633c2c83e3da42a502f52466022480f4208261de"
+
+json3@3.3.2:
+  version "3.3.2"
+  resolved "https://registry.yarnpkg.com/json3/-/json3-3.3.2.tgz#3c0434743df93e2f5c42aee7b19bcb483575f4e1"
+
+levn@~0.3.0:
+  version "0.3.0"
+  resolved "https://registry.yarnpkg.com/levn/-/levn-0.3.0.tgz#3b09924edf9f083c0490fdd4c0bc4421e04764ee"
+  dependencies:
+    prelude-ls "~1.1.2"
+    type-check "~0.3.2"
+
+lodash._baseassign@^3.0.0:
+  version "3.2.0"
+  resolved "https://registry.yarnpkg.com/lodash._baseassign/-/lodash._baseassign-3.2.0.tgz#8c38a099500f215ad09e59f1722fd0c52bfe0a4e"
+  dependencies:
+    lodash._basecopy "^3.0.0"
+    lodash.keys "^3.0.0"
+
+lodash._basecopy@^3.0.0:
+  version "3.0.1"
+  resolved "https://registry.yarnpkg.com/lodash._basecopy/-/lodash._basecopy-3.0.1.tgz#8da0e6a876cf344c0ad8a54882111dd3c5c7ca36"
+
+lodash._basecreate@^3.0.0:
+  version "3.0.3"
+  resolved "https://registry.yarnpkg.com/lodash._basecreate/-/lodash._basecreate-3.0.3.tgz#1bc661614daa7fc311b7d03bf16806a0213cf821"
+
+lodash._getnative@^3.0.0:
+  version "3.9.1"
+  resolved "https://registry.yarnpkg.com/lodash._getnative/-/lodash._getnative-3.9.1.tgz#570bc7dede46d61cdcde687d65d3eecbaa3aaff5"
+
+lodash._isiterateecall@^3.0.0:
+  version "3.0.9"
+  resolved "https://registry.yarnpkg.com/lodash._isiterateecall/-/lodash._isiterateecall-3.0.9.tgz#5203ad7ba425fae842460e696db9cf3e6aac057c"
+
+lodash.create@3.1.1:
+  version "3.1.1"
+  resolved "https://registry.yarnpkg.com/lodash.create/-/lodash.create-3.1.1.tgz#d7f2849f0dbda7e04682bb8cd72ab022461debe7"
+  dependencies:
+    lodash._baseassign "^3.0.0"
+    lodash._basecreate "^3.0.0"
+    lodash._isiterateecall "^3.0.0"
+
+lodash.isarguments@^3.0.0:
+  version "3.1.0"
+  resolved "https://registry.yarnpkg.com/lodash.isarguments/-/lodash.isarguments-3.1.0.tgz#2f573d85c6a24289ff00663b491c1d338ff3458a"
+
+lodash.isarray@^3.0.0:
+  version "3.0.4"
+  resolved "https://registry.yarnpkg.com/lodash.isarray/-/lodash.isarray-3.0.4.tgz#79e4eb88c36a8122af86f844aa9bcd851b5fbb55"
+
+lodash.keys@^3.0.0:
+  version "3.1.2"
+  resolved "https://registry.yarnpkg.com/lodash.keys/-/lodash.keys-3.1.2.tgz#4dbc0472b156be50a0b286855d1bd0b0c656098a"
+  dependencies:
+    lodash._getnative "^3.0.0"
+    lodash.isarguments "^3.0.0"
+    lodash.isarray "^3.0.0"
+
+minimatch@^3.0.2:
+  version "3.0.3"
+  resolved "https://registry.yarnpkg.com/minimatch/-/minimatch-3.0.3.tgz#2a4e4090b96b2db06a9d7df01055a62a77c9b774"
+  dependencies:
+    brace-expansion "^1.0.0"
+
+minimist@0.0.8:
+  version "0.0.8"
+  resolved "https://registry.yarnpkg.com/minimist/-/minimist-0.0.8.tgz#857fcabfc3397d2625b8228262e86aa7a011b05d"
+
+mkdirp@0.5.1:
+  version "0.5.1"
+  resolved "https://registry.yarnpkg.com/mkdirp/-/mkdirp-0.5.1.tgz#30057438eac6cf7f8c4767f38648d6697d75c903"
+  dependencies:
+    minimist "0.0.8"
+
+mocha@*:
+  version "3.1.2"
+  resolved "https://registry.yarnpkg.com/mocha/-/mocha-3.1.2.tgz#51f93b432bf7e1b175ffc22883ccd0be32dba6b5"
+  dependencies:
+    browser-stdout "1.3.0"
+    commander "2.9.0"
+    debug "2.2.0"
+    diff "1.4.0"
+    escape-string-regexp "1.0.5"
+    glob "7.0.5"
+    growl "1.9.2"
+    json3 "3.3.2"
+    lodash.create "3.1.1"
+    mkdirp "0.5.1"
+    supports-color "3.1.2"
+
+ms@0.7.1:
+  version "0.7.1"
+  resolved "https://registry.yarnpkg.com/ms/-/ms-0.7.1.tgz#9cd13c03adbff25b65effde7ce864ee952017098"
+
+once@^1.3.0:
+  version "1.4.0"
+  resolved "https://registry.yarnpkg.com/once/-/once-1.4.0.tgz#583b1aa775961d4b113ac17d9c50baef9dd76bd1"
+  dependencies:
+    wrappy "1"
+
+optionator@^0.8.1:
+  version "0.8.2"
+  resolved "https://registry.yarnpkg.com/optionator/-/optionator-0.8.2.tgz#364c5e409d3f4d6301d6c0b4c05bba50180aeb64"
+  dependencies:
+    deep-is "~0.1.3"
+    fast-levenshtein "~2.0.4"
+    levn "~0.3.0"
+    prelude-ls "~1.1.2"
+    type-check "~0.3.2"
+    wordwrap "~1.0.0"
+
+path-is-absolute@^1.0.0:
+  version "1.0.1"
+  resolved "https://registry.yarnpkg.com/path-is-absolute/-/path-is-absolute-1.0.1.tgz#174b9268735534ffbc7ace6bf53a5a9e1b5c5f5f"
+
+prelude-ls@~1.1.2:
+  version "1.1.2"
+  resolved "https://registry.yarnpkg.com/prelude-ls/-/prelude-ls-1.1.2.tgz#21932a549f5e52ffd9a827f570e04be62a97da54"
+
+rx@^4.1.0:
+  version "4.1.0"
+  resolved "https://registry.yarnpkg.com/rx/-/rx-4.1.0.tgz#a5f13ff79ef3b740fe30aa803fb09f98805d4782"
+
+source-map@~0.2.0:
+  version "0.2.0"
+  resolved "https://registry.yarnpkg.com/source-map/-/source-map-0.2.0.tgz#dab73fbcfc2ba819b4de03bd6f6eaa48164b3f9d"
+  dependencies:
+    amdefine ">=0.0.4"
+
+supports-color@3.1.2:
+  version "3.1.2"
+  resolved "https://registry.yarnpkg.com/supports-color/-/supports-color-3.1.2.tgz#72a262894d9d408b956ca05ff37b2ed8a6e2a2d5"
+  dependencies:
+    has-flag "^1.0.0"
+
+type-check@~0.3.2:
+  version "0.3.2"
+  resolved "https://registry.yarnpkg.com/type-check/-/type-check-0.3.2.tgz#5884cab512cf1d355e3fb784f30804b2b520db72"
+  dependencies:
+    prelude-ls "~1.1.2"
+
+type-detect@^1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/type-detect/-/type-detect-1.0.0.tgz#762217cc06db258ec48908a1298e8b95121e8ea2"
+
+type-detect@0.1.1:
+  version "0.1.1"
+  resolved "https://registry.yarnpkg.com/type-detect/-/type-detect-0.1.1.tgz#0ba5ec2a885640e470ea4e8505971900dac58822"
+
+wordwrap@~1.0.0:
+  version "1.0.0"
+  resolved "https://registry.yarnpkg.com/wordwrap/-/wordwrap-1.0.0.tgz#27584810891456a4171c8d0226441ade90cbcaeb"
+
+wrappy@1:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/wrappy/-/wrappy-1.0.2.tgz#b5243d8f3ec1aa35f1364605bc0d1036e30ab69f"
+