diff --git a/.babelrc b/.babelrc
index 84b1bcc..eb1f74d 100644
--- a/.babelrc
+++ b/.babelrc
@@ -1,5 +1,5 @@
 {
-  "presets": ["env"],
+  "presets": ["env", "flow"],
   "env": {
     "test": {
       "plugins": ["istanbul"]
diff --git a/.eslintrc.json b/.eslintrc.json
index bfd589d..c8a0431 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -1,8 +1,13 @@
 {
+  "plugins": ["flowtype"],
+  "parser": "babel-eslint",
   "parserOptions": {
       "ecmaVersion": 8,
       "sourceType": "module"
   },
+  "extends": [
+    "plugin:flowtype/recommended"
+  ],
   "rules": {
     "no-alert": 2,
     "no-array-constructor": 0,
diff --git a/.flowconfig b/.flowconfig
new file mode 100644
index 0000000..0d26140
--- /dev/null
+++ b/.flowconfig
@@ -0,0 +1,12 @@
+[ignore]
+
+[include]
+
+[libs]
+flow-typed
+
+[lints]
+
+[options]
+
+[strict]
diff --git a/.gitignore b/.gitignore
index 1d56f7b..039924f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,6 +3,8 @@ node_modules
 coverage
 examples/*.png
 browser\.js
+browser\.js\.flow
 dist
 package-lock\.json
 \.nyc_output
+flow-typed/npm
diff --git a/flow-typed/pngjs-types.js b/flow-typed/pngjs-types.js
new file mode 100644
index 0000000..a94e157
--- /dev/null
+++ b/flow-typed/pngjs-types.js
@@ -0,0 +1,13 @@
+//  @flow
+
+declare type Metadata = {|
+  width: number,
+  height: number,
+  depth: 1 | 2 | 4 | 8 | 16,
+  interlace: boolean,
+  palette: boolean,
+  color: boolean,
+  alpha: boolean,
+  bpp: 1 | 2 | 3 | 4,
+  colorType: 0 | 2 | 3 | 4 | 6,
+|}
diff --git a/lib/png.js b/lib/png.js
index 8978867..fdf01d4 100644
--- a/lib/png.js
+++ b/lib/png.js
@@ -1,28 +1,40 @@
-import Stream from 'stream';
+// @flow
+import Stream, { type Readable, type Writable } from 'stream';
 import { ParserAsync as Parser } from './parser';
 import { PackerAsync as Packer } from './packer';
 import * as PNGSync from './png-sync';
 import * as propData from './propData';
 
+type Props = {
+  width?: number,
+  height?: number,
+  initGrayscaleData?: boolean,
+  initPropData?: boolean | { shrinkMax: boolean, shrinkMin: boolean },
+}
+
+// $FlowFixMe
 export class PNG extends Stream {
-  constructor(options) {
+  width: number;
+  height: number;
+  color: boolean;
+  depth: number;
+  _grayscaleData: Uint8Array | Uint16Array | void;
+  _propData: ?Float32Array;
+  data: ?Buffer;
+  gamma: number;
+
+  constructor(options: Props = {}) {
     super(options);
-    Stream.call(this);
-
-    options = options || {}; // eslint-disable-line no-param-reassign
+    const {
+      width, height,
+      initGrayscaleData, initPropData,
+    } = options;
 
     // coerce pixel dimensions to integers (also coerces undefined -> 0):
-    this.width = options.width | 0;
-    this.height = options.height | 0;
+    this.width = width || 0;
+    this.height = height || 0;
 
-    this.color = undefined;
-    this.depth = undefined;
-    this._grayscaleData = undefined;
-    this._propData = undefined;
-    this._configPostParse = {
-      initGrayscaleData: options.initGrayscaleData,
-      initPropData: options.initPropData,
-    };
+    this._configPostParse = { initGrayscaleData, initPropData };
 
     this.data = this.width > 0 && this.height > 0 ?
       new Buffer(4 * this.width * this.height) : null;
@@ -56,6 +68,7 @@ export class PNG extends Stream {
     this._postParsed = this._postParsed.bind(this);
   }
 
+  _postParsed: Function;
   _postParsed() {
     this._grayscaleData = undefined;
     this._propData = undefined;
@@ -83,7 +96,7 @@ export class PNG extends Stream {
     return this;
   }
 
-  parse(data, callback) {
+  parse(data: ArrayBuffer | Readable, callback: Function) {
     if (callback) {
       let onParsed, onError;
 
@@ -107,16 +120,16 @@ export class PNG extends Stream {
     return this;
   }
 
-  write(data) {
+  write(data: Writable) {
     this._parser.write(data);
     return true;
   }
 
-  end(data) {
+  end(data: Readable | ArrayBuffer) {
     this._parser.end(data);
   }
 
-  _metadata(metadata) {
+  _metadata(metadata: Metadata) {
     const { width, height, color, depth } = metadata;
     this.width = width;
     this.height = height;
@@ -126,7 +139,7 @@ export class PNG extends Stream {
     this.emit('metadata', metadata);
   }
 
-  _gamma(gamma) {
+  _gamma(gamma: number) {
     this.gamma = gamma;
   }
 
@@ -136,7 +149,13 @@ export class PNG extends Stream {
     }
   }
 
-  bitblt(src, dst, srcX = 0, srcY = 0, width = 0, height = 0, deltaX = 0, deltaY = 0) { // eslint-disable-line max-params
+  // eslint-disable-next-line max-params
+  bitblt(
+    src: PNG, dst: PNG,
+    srcX: number = 0, srcY: number = 0,
+    width: number = 0, height: number = 0,
+    deltaX: number = 0, deltaY: number = 0,
+  ) {
     // coerce pixel dimensions to integers (also coerces undefined -> 0):
 
     if (srcX > src.width || srcY > src.height || srcX + width > src.width || srcY + height > src.height) {
@@ -147,8 +166,17 @@ export class PNG extends Stream {
       throw new Error('bitblt writing outside image');
     }
 
+    const { data } = src;
+    if (!data) {
+      throw new Error('No data available in src');
+    }
+    const { data: outData } = dst;
+    if (!outData) {
+      throw new Error('No data available in dst');
+    }
+
     for (var y = 0; y < height; y++) {
-      src.data.copy(dst.data,
+      data.copy(outData,
         ((deltaY + y) * dst.width + deltaX) << 2,
         ((srcY + y) * src.width + srcX) << 2,
         ((srcY + y) * src.width + srcX + width) << 2
@@ -158,19 +186,25 @@ export class PNG extends Stream {
     return this;
   }
 
-  adjustGamma(src) {
+  adjustGamma(src: PNG) {
     if (src.gamma) {
+      const { data } = src;
+      if (!data) {
+        throw new Error('No data available for object');
+      }
+
       for (var y = 0; y < src.height; y++) {
         for (var x = 0; x < src.width; x++) {
           var idx = (src.width * y + x) << 2;
 
           for (var i = 0; i < 3; i++) {
-            var sample = src.data[idx + i] / 255;
+            var sample = data[idx + i] / 255;
             sample = Math.pow(sample, 1 / 2.2 / src.gamma);
-            src.data[idx + i] = Math.round(sample * 255);
+            data[idx + i] = Math.round(sample * 255);
           }
         }
       }
+      src.data = data;
       src.gamma = 0;
     }
     return this;
@@ -178,12 +212,17 @@ export class PNG extends Stream {
 
   initGrayscaleData() {
     const { data } = this;
+    if (!data) {
+      throw new Error('The initGrayscaleData() called before receiving data');
+    }
+
+    let outData;
     if (this.color) {
       const mono = ({ red, green, blue }) => ((0.2125 * red) + (0.7154 * green) + (0.0721 * blue));
-      this._grayscaleData = data.slice(data.length / 4);
-      for (let i = 0; i < this._grayscaleData.length; i += 1) {
+      outData = data.slice(data.length / 4);
+      for (let i = 0; i < outData.length; i += 1) {
         const pxPos = i * 4;
-        this._grayscaleData[i] = mono({
+        outData[i] = mono({
           red: data[pxPos + 0],
           green: data[pxPos + 1],
           blue: data[pxPos + 2],
@@ -191,8 +230,10 @@ export class PNG extends Stream {
       }
     }
     else {
-      this._grayscaleData = data.filter((clr, i) => i % 4 === 0);
+      outData = data.filter((clr, i) => i % 4 === 0);
     }
+
+    this._grayscaleData = outData;
   }
 
   // Retrieve mono data without aplpha channel
@@ -209,7 +250,7 @@ export class PNG extends Stream {
     return this._grayscaleData;
   }
 
-  initPropData(shrinkMin = false, shrinkMax = false) {
+  initPropData(shrinkMin: boolean = false, shrinkMax: boolean = false) {
     if (this.color) {
       this._propData = propData.color(
         this.data,
@@ -239,7 +280,7 @@ export class PNG extends Stream {
   // Retrieve colors as proportions instead of integers
   // if you want to limit the max proporiton to the bufferEqual
   // max/min value then set the shrinkMax/shrinkMin.
-  propData(shrinkMin = false, shrinkMax = false) {
+  propData(shrinkMin: boolean = false, shrinkMax: boolean = false) {
     const { data } = this;
     if (!data) {
       throw new Error('Invalid call - no data to convert');
diff --git a/package.json b/package.json
index a1ece37..b615af3 100644
--- a/package.json
+++ b/package.json
@@ -40,11 +40,12 @@
     "test": "test"
   },
   "scripts": {
-    "build": "npm run compile && npm run browserify",
+    "build": "npm run compile && npm run build:flow && npm run build:browserify",
+    "build:flow": "flow-copy-source -v -i 'test/**' lib dist",
+    "build:clean": "rimraf dist",
+    "build:browserify": "browserify dist/png.js --standalone png > browser.js && cp dist/png.js.flow browser.js.flow",
     "prepublish": "npm run build",
-    "clean:dist": "rimraf dist",
-    "compile": "npm run clean:dist && babel -d dist/ lib/",
-    "browserify": "browserify dist/png.js --standalone png > browser.js",
+    "compile": "npm run build:clean && babel -d dist/ lib/",
     "coverage": "NODE_ENV=test nyc babel-tape-runner test/*-spec.js nolarge| tap-nyc",
     "coveralls": "nyc report --reporter=text-lcov | coveralls",
     "monitor": "nodemon --watch lib --delay 2.5s --exec \"npm run build\"",
@@ -67,8 +68,10 @@
   },
   "devDependencies": {
     "babel-cli": "^6.26.0",
+    "babel-eslint": "^8.1.2",
     "babel-plugin-istanbul": "^4.1.5",
     "babel-preset-env": "^1.6.1",
+    "babel-preset-flow": "^6.23.0",
     "babel-register": "^6.26.0",
     "babel-tape-runner": "^2.0.1",
     "browserify": "^14.5.0",
@@ -76,6 +79,9 @@
     "connect": "^3.6.5",
     "coveralls": "^3.0.0",
     "eslint": "^4.14.0",
+    "eslint-plugin-flowtype": "^2.40.1",
+    "flow-bin": "^0.61.0",
+    "flow-copy-source": "^1.2.1",
     "istanbul": "^0.4.4",
     "nodemon": "^1.14.3",
     "nyc": "^11.4.1",
diff --git a/yarn.lock b/yarn.lock
index 317141b..ebed511 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2,6 +2,59 @@
 # yarn lockfile v1
 
 
+"@babel/code-frame@7.0.0-beta.31":
+  version "7.0.0-beta.31"
+  resolved "https://registry.yarnpkg.com/@babel/code-frame/-/code-frame-7.0.0-beta.31.tgz#473d021ecc573a2cce1c07d5b509d5215f46ba35"
+  dependencies:
+    chalk "^2.0.0"
+    esutils "^2.0.2"
+    js-tokens "^3.0.0"
+
+"@babel/helper-function-name@7.0.0-beta.31":
+  version "7.0.0-beta.31"
+  resolved "https://registry.yarnpkg.com/@babel/helper-function-name/-/helper-function-name-7.0.0-beta.31.tgz#afe63ad799209989348b1109b44feb66aa245f57"
+  dependencies:
+    "@babel/helper-get-function-arity" "7.0.0-beta.31"
+    "@babel/template" "7.0.0-beta.31"
+    "@babel/traverse" "7.0.0-beta.31"
+    "@babel/types" "7.0.0-beta.31"
+
+"@babel/helper-get-function-arity@7.0.0-beta.31":
+  version "7.0.0-beta.31"
+  resolved "https://registry.yarnpkg.com/@babel/helper-get-function-arity/-/helper-get-function-arity-7.0.0-beta.31.tgz#1176d79252741218e0aec872ada07efb2b37a493"
+  dependencies:
+    "@babel/types" "7.0.0-beta.31"
+
+"@babel/template@7.0.0-beta.31":
+  version "7.0.0-beta.31"
+  resolved "https://registry.yarnpkg.com/@babel/template/-/template-7.0.0-beta.31.tgz#577bb29389f6c497c3e7d014617e7d6713f68bda"
+  dependencies:
+    "@babel/code-frame" "7.0.0-beta.31"
+    "@babel/types" "7.0.0-beta.31"
+    babylon "7.0.0-beta.31"
+    lodash "^4.2.0"
+
+"@babel/traverse@7.0.0-beta.31":
+  version "7.0.0-beta.31"
+  resolved "https://registry.yarnpkg.com/@babel/traverse/-/traverse-7.0.0-beta.31.tgz#db399499ad74aefda014f0c10321ab255134b1df"
+  dependencies:
+    "@babel/code-frame" "7.0.0-beta.31"
+    "@babel/helper-function-name" "7.0.0-beta.31"
+    "@babel/types" "7.0.0-beta.31"
+    babylon "7.0.0-beta.31"
+    debug "^3.0.1"
+    globals "^10.0.0"
+    invariant "^2.2.0"
+    lodash "^4.2.0"
+
+"@babel/types@7.0.0-beta.31":
+  version "7.0.0-beta.31"
+  resolved "https://registry.yarnpkg.com/@babel/types/-/types-7.0.0-beta.31.tgz#42c9c86784f674c173fb21882ca9643334029de4"
+  dependencies:
+    esutils "^2.0.2"
+    lodash "^4.2.0"
+    to-fast-properties "^2.0.0"
+
 JSONStream@^1.0.3:
   version "1.3.2"
   resolved "https://registry.yarnpkg.com/JSONStream/-/JSONStream-1.3.2.tgz#c102371b6ec3a7cf3b847ca00c20bb0fce4c6dea"
@@ -274,6 +327,17 @@ babel-core@^6.26.0:
     slash "^1.0.0"
     source-map "^0.5.6"
 
+babel-eslint@^8.1.2:
+  version "8.1.2"
+  resolved "https://registry.yarnpkg.com/babel-eslint/-/babel-eslint-8.1.2.tgz#a39230b0c20ecbaa19a35d5633bf9b9ca2c8116f"
+  dependencies:
+    "@babel/code-frame" "7.0.0-beta.31"
+    "@babel/traverse" "7.0.0-beta.31"
+    "@babel/types" "7.0.0-beta.31"
+    babylon "7.0.0-beta.31"
+    eslint-scope "~3.7.1"
+    eslint-visitor-keys "^1.0.0"
+
 babel-generator@^6.18.0, babel-generator@^6.26.0:
   version "6.26.0"
   resolved "https://registry.yarnpkg.com/babel-generator/-/babel-generator-6.26.0.tgz#ac1ae20070b79f6e3ca1d3269613053774f20dc5"
@@ -416,6 +480,10 @@ babel-plugin-syntax-exponentiation-operator@^6.8.0:
   version "6.13.0"
   resolved "https://registry.yarnpkg.com/babel-plugin-syntax-exponentiation-operator/-/babel-plugin-syntax-exponentiation-operator-6.13.0.tgz#9ee7e8337290da95288201a6a57f4170317830de"
 
+babel-plugin-syntax-flow@^6.18.0:
+  version "6.18.0"
+  resolved "https://registry.yarnpkg.com/babel-plugin-syntax-flow/-/babel-plugin-syntax-flow-6.18.0.tgz#4c3ab20a2af26aa20cd25995c398c4eb70310c8d"
+
 babel-plugin-syntax-trailing-function-commas@^6.22.0:
   version "6.22.0"
   resolved "https://registry.yarnpkg.com/babel-plugin-syntax-trailing-function-commas/-/babel-plugin-syntax-trailing-function-commas-6.22.0.tgz#ba0360937f8d06e40180a43fe0d5616fff532cf3"
@@ -604,6 +672,13 @@ babel-plugin-transform-exponentiation-operator@^6.22.0:
     babel-plugin-syntax-exponentiation-operator "^6.8.0"
     babel-runtime "^6.22.0"
 
+babel-plugin-transform-flow-strip-types@^6.22.0:
+  version "6.22.0"
+  resolved "https://registry.yarnpkg.com/babel-plugin-transform-flow-strip-types/-/babel-plugin-transform-flow-strip-types-6.22.0.tgz#84cb672935d43714fdc32bce84568d87441cf7cf"
+  dependencies:
+    babel-plugin-syntax-flow "^6.18.0"
+    babel-runtime "^6.22.0"
+
 babel-plugin-transform-regenerator@^6.22.0:
   version "6.26.0"
   resolved "https://registry.yarnpkg.com/babel-plugin-transform-regenerator/-/babel-plugin-transform-regenerator-6.26.0.tgz#e0703696fbde27f0a3efcacf8b4dca2f7b3a8f2f"
@@ -660,6 +735,12 @@ babel-preset-env@^1.6.1:
     invariant "^2.2.2"
     semver "^5.3.0"
 
+babel-preset-flow@^6.23.0:
+  version "6.23.0"
+  resolved "https://registry.yarnpkg.com/babel-preset-flow/-/babel-preset-flow-6.23.0.tgz#e71218887085ae9a24b5be4169affb599816c49d"
+  dependencies:
+    babel-plugin-transform-flow-strip-types "^6.22.0"
+
 babel-register@^6.26.0, babel-register@^6.3.13:
   version "6.26.0"
   resolved "https://registry.yarnpkg.com/babel-register/-/babel-register-6.26.0.tgz#6ed021173e2fcb486d7acb45c6009a856f647071"
@@ -720,6 +801,10 @@ babel-types@^6.18.0, babel-types@^6.19.0, babel-types@^6.24.1, babel-types@^6.26
     lodash "^4.17.4"
     to-fast-properties "^1.0.3"
 
+babylon@7.0.0-beta.31:
+  version "7.0.0-beta.31"
+  resolved "https://registry.yarnpkg.com/babylon/-/babylon-7.0.0-beta.31.tgz#7ec10f81e0e456fd0f855ad60fa30c2ac454283f"
+
 babylon@^6.18.0:
   version "6.18.0"
   resolved "https://registry.yarnpkg.com/babylon/-/babylon-6.18.0.tgz#af2f3b88fa6f5c1e4c634d1a0f8eac4f55b395e3"
@@ -1314,7 +1399,7 @@ debug@2.6.9, debug@^2.2.0, debug@^2.6.8:
   dependencies:
     ms "2.0.0"
 
-debug@^3.1.0:
+debug@^3.0.1, debug@^3.1.0:
   version "3.1.0"
   resolved "https://registry.yarnpkg.com/debug/-/debug-3.1.0.tgz#5bb5a0672628b64149566ba16819e61518c67261"
   dependencies:
@@ -1528,7 +1613,13 @@ escodegen@1.8.x:
   optionalDependencies:
     source-map "~0.2.0"
 
-eslint-scope@^3.7.1:
+eslint-plugin-flowtype@^2.40.1:
+  version "2.40.1"
+  resolved "https://registry.yarnpkg.com/eslint-plugin-flowtype/-/eslint-plugin-flowtype-2.40.1.tgz#f78a8e6a4cc6da831dd541eb61e803ff0279b796"
+  dependencies:
+    lodash "^4.15.0"
+
+eslint-scope@^3.7.1, eslint-scope@~3.7.1:
   version "3.7.1"
   resolved "https://registry.yarnpkg.com/eslint-scope/-/eslint-scope-3.7.1.tgz#3d63c3edfda02e06e01a452ad88caacc7cdcb6e8"
   dependencies:
@@ -1794,7 +1885,7 @@ find-up@^1.0.0:
     path-exists "^2.0.0"
     pinkie-promise "^2.0.0"
 
-find-up@^2.1.0:
+find-up@^2.0.0, find-up@^2.1.0:
   version "2.1.0"
   resolved "https://registry.yarnpkg.com/find-up/-/find-up-2.1.0.tgz#45d1b7e506c717ddd482775a2b77920a3c0c57a7"
   dependencies:
@@ -1809,6 +1900,20 @@ flat-cache@^1.2.1:
     graceful-fs "^4.1.2"
     write "^0.2.1"
 
+flow-bin@^0.61.0:
+  version "0.61.0"
+  resolved "https://registry.yarnpkg.com/flow-bin/-/flow-bin-0.61.0.tgz#d0473a8c35dbbf4de573823f4932124397d32d35"
+
+flow-copy-source@^1.2.1:
+  version "1.2.1"
+  resolved "https://registry.yarnpkg.com/flow-copy-source/-/flow-copy-source-1.2.1.tgz#705c2fa8fb29a281118e1c4b66218dec24b745ec"
+  dependencies:
+    chokidar "^1.7.0"
+    fs-extra "^3.0.1"
+    glob "^7.0.0"
+    kefir "^3.7.3"
+    yargs "^8.0.2"
+
 for-each@~0.3.2:
   version "0.3.2"
   resolved "https://registry.yarnpkg.com/for-each/-/for-each-0.3.2.tgz#2c40450b9348e97f281322593ba96704b9abd4d4"
@@ -1872,6 +1977,14 @@ fs-extra@^1.0.0:
     jsonfile "^2.1.0"
     klaw "^1.0.0"
 
+fs-extra@^3.0.1:
+  version "3.0.1"
+  resolved "https://registry.yarnpkg.com/fs-extra/-/fs-extra-3.0.1.tgz#3794f378c58b342ea7dbbb23095109c4b3b62291"
+  dependencies:
+    graceful-fs "^4.1.2"
+    jsonfile "^3.0.0"
+    universalify "^0.1.0"
+
 fs-readdir-recursive@^1.0.0:
   version "1.1.0"
   resolved "https://registry.yarnpkg.com/fs-readdir-recursive/-/fs-readdir-recursive-1.1.0.tgz#e32fc030a2ccee44a6b5371308da54be0b397d27"
@@ -1972,25 +2085,25 @@ glob@^6.0.1:
     once "^1.3.0"
     path-is-absolute "^1.0.0"
 
-glob@^7.0.3, glob@^7.0.5:
-  version "7.1.1"
-  resolved "https://registry.yarnpkg.com/glob/-/glob-7.1.1.tgz#805211df04faaf1c63a3600306cdf5ade50b2ec8"
+glob@^7.0.0, glob@^7.0.6, glob@^7.1.0, glob@^7.1.2, glob@~7.1.2:
+  version "7.1.2"
+  resolved "https://registry.yarnpkg.com/glob/-/glob-7.1.2.tgz#c19c9df9a028702d678612384a6552404c636d15"
   dependencies:
     fs.realpath "^1.0.0"
     inflight "^1.0.4"
     inherits "2"
-    minimatch "^3.0.2"
+    minimatch "^3.0.4"
     once "^1.3.0"
     path-is-absolute "^1.0.0"
 
-glob@^7.0.6, glob@^7.1.0, glob@^7.1.2, glob@~7.1.2:
-  version "7.1.2"
-  resolved "https://registry.yarnpkg.com/glob/-/glob-7.1.2.tgz#c19c9df9a028702d678612384a6552404c636d15"
+glob@^7.0.3, glob@^7.0.5:
+  version "7.1.1"
+  resolved "https://registry.yarnpkg.com/glob/-/glob-7.1.1.tgz#805211df04faaf1c63a3600306cdf5ade50b2ec8"
   dependencies:
     fs.realpath "^1.0.0"
     inflight "^1.0.4"
     inherits "2"
-    minimatch "^3.0.4"
+    minimatch "^3.0.2"
     once "^1.3.0"
     path-is-absolute "^1.0.0"
 
@@ -2000,6 +2113,10 @@ global-dirs@^0.1.0:
   dependencies:
     ini "^1.3.4"
 
+globals@^10.0.0:
+  version "10.4.0"
+  resolved "https://registry.yarnpkg.com/globals/-/globals-10.4.0.tgz#5c477388b128a9e4c5c5d01c7a2aca68c68b2da7"
+
 globals@^11.0.1:
   version "11.1.0"
   resolved "https://registry.yarnpkg.com/globals/-/globals-11.1.0.tgz#632644457f5f0e3ae711807183700ebf2e4633e4"
@@ -2295,7 +2412,7 @@ insert-module-globals@^7.0.0:
     through2 "^2.0.0"
     xtend "^4.0.0"
 
-invariant@^2.2.2:
+invariant@^2.2.0, invariant@^2.2.2:
   version "2.2.2"
   resolved "https://registry.yarnpkg.com/invariant/-/invariant-2.2.2.tgz#9e1f56ac0acdb6bf303306f338be3b204ae60360"
   dependencies:
@@ -2642,6 +2759,12 @@ jsonfile@^2.1.0:
   optionalDependencies:
     graceful-fs "^4.1.6"
 
+jsonfile@^3.0.0:
+  version "3.0.1"
+  resolved "https://registry.yarnpkg.com/jsonfile/-/jsonfile-3.0.1.tgz#a5ecc6f65f53f662c4415c7675a0331d0992ec66"
+  optionalDependencies:
+    graceful-fs "^4.1.6"
+
 jsonify@~0.0.0:
   version "0.0.0"
   resolved "https://registry.yarnpkg.com/jsonify/-/jsonify-0.0.0.tgz#2c74b6ee41d93ca51b7b5aaee8f503631d252a73"
@@ -2659,6 +2782,12 @@ jsprim@^1.2.2:
     json-schema "0.2.3"
     verror "1.3.6"
 
+kefir@^3.7.3:
+  version "3.8.0"
+  resolved "https://registry.yarnpkg.com/kefir/-/kefir-3.8.0.tgz#63b5dce575f1a7ab3286788e771eb104b181b676"
+  dependencies:
+    symbol-observable "1.0.4"
+
 kew@^0.7.0:
   version "0.7.0"
   resolved "https://registry.yarnpkg.com/kew/-/kew-0.7.0.tgz#79d93d2d33363d6fdd2970b335d9141ad591d79b"
@@ -2732,6 +2861,15 @@ load-json-file@^1.0.0:
     pinkie-promise "^2.0.0"
     strip-bom "^2.0.0"
 
+load-json-file@^2.0.0:
+  version "2.0.0"
+  resolved "https://registry.yarnpkg.com/load-json-file/-/load-json-file-2.0.0.tgz#7947e42149af80d696cbf797bcaabcfe1fe29ca8"
+  dependencies:
+    graceful-fs "^4.1.2"
+    parse-json "^2.2.0"
+    pify "^2.0.0"
+    strip-bom "^3.0.0"
+
 locate-path@^2.0.0:
   version "2.0.0"
   resolved "https://registry.yarnpkg.com/locate-path/-/locate-path-2.0.0.tgz#2b568b265eec944c6d9c0de9c3dbbbca0354cd8e"
@@ -2743,7 +2881,7 @@ lodash.memoize@~3.0.3:
   version "3.0.4"
   resolved "https://registry.yarnpkg.com/lodash.memoize/-/lodash.memoize-3.0.4.tgz#2dcbd2c287cbc0a55cc42328bd0c736150d53e3f"
 
-lodash@^4.17.4, lodash@^4.3.0:
+lodash@^4.15.0, lodash@^4.17.4, lodash@^4.2.0, lodash@^4.3.0:
   version "4.17.4"
   resolved "https://registry.yarnpkg.com/lodash/-/lodash-4.17.4.tgz#78203a4d1c328ae1d86dca6460e369b57f4055ae"
 
@@ -3256,6 +3394,12 @@ path-type@^1.0.0:
     pify "^2.0.0"
     pinkie-promise "^2.0.0"
 
+path-type@^2.0.0:
+  version "2.0.0"
+  resolved "https://registry.yarnpkg.com/path-type/-/path-type-2.0.0.tgz#f012ccb8415b7096fc2daa1054c3d72389594c73"
+  dependencies:
+    pify "^2.0.0"
+
 pause-stream@0.0.11:
   version "0.0.11"
   resolved "https://registry.yarnpkg.com/pause-stream/-/pause-stream-0.0.11.tgz#fe5a34b0cbce12b5aa6a2b403ee2e73b602f1445"
@@ -3470,6 +3614,13 @@ read-pkg-up@^1.0.1:
     find-up "^1.0.0"
     read-pkg "^1.0.0"
 
+read-pkg-up@^2.0.0:
+  version "2.0.0"
+  resolved "https://registry.yarnpkg.com/read-pkg-up/-/read-pkg-up-2.0.0.tgz#6b72a8048984e0c41e79510fd5e9fa99b3b549be"
+  dependencies:
+    find-up "^2.0.0"
+    read-pkg "^2.0.0"
+
 read-pkg@^1.0.0:
   version "1.1.0"
   resolved "https://registry.yarnpkg.com/read-pkg/-/read-pkg-1.1.0.tgz#f5ffaa5ecd29cb31c0474bca7d756b6bb29e3f28"
@@ -3478,6 +3629,14 @@ read-pkg@^1.0.0:
     normalize-package-data "^2.3.2"
     path-type "^1.0.0"
 
+read-pkg@^2.0.0:
+  version "2.0.0"
+  resolved "https://registry.yarnpkg.com/read-pkg/-/read-pkg-2.0.0.tgz#8ef1c0623c6a6db0dc6713c4bfac46332b2368f8"
+  dependencies:
+    load-json-file "^2.0.0"
+    normalize-package-data "^2.3.2"
+    path-type "^2.0.0"
+
 readable-stream@^2.0.0, readable-stream@^2.1.5, readable-stream@^2.2.2:
   version "2.2.6"
   resolved "https://registry.yarnpkg.com/readable-stream/-/readable-stream-2.2.6.tgz#8b43aed76e71483938d12a8d46c6cf1a00b1f816"
@@ -4044,6 +4203,10 @@ strip-bom@^2.0.0:
   dependencies:
     is-utf8 "^0.2.0"
 
+strip-bom@^3.0.0:
+  version "3.0.0"
+  resolved "https://registry.yarnpkg.com/strip-bom/-/strip-bom-3.0.0.tgz#2334c18e9c759f7bdd56fdef7e9ae3d588e68ed3"
+
 strip-eof@^1.0.0:
   version "1.0.0"
   resolved "https://registry.yarnpkg.com/strip-eof/-/strip-eof-1.0.0.tgz#bb43ff5598a6eb05d89b59fcd129c983313606bf"
@@ -4074,6 +4237,10 @@ supports-color@^4.0.0:
   dependencies:
     has-flag "^2.0.0"
 
+symbol-observable@1.0.4:
+  version "1.0.4"
+  resolved "https://registry.yarnpkg.com/symbol-observable/-/symbol-observable-1.0.4.tgz#29bf615d4aa7121bdd898b22d4b3f9bc4e2aa03d"
+
 syntax-error@^1.1.1:
   version "1.3.0"
   resolved "https://registry.yarnpkg.com/syntax-error/-/syntax-error-1.3.0.tgz#1ed9266c4d40be75dc55bf9bb1cb77062bb96ca1"
@@ -4218,6 +4385,10 @@ to-fast-properties@^1.0.3:
   version "1.0.3"
   resolved "https://registry.yarnpkg.com/to-fast-properties/-/to-fast-properties-1.0.3.tgz#b83571fa4d8c25b82e231b06e3a3055de4ca1a47"
 
+to-fast-properties@^2.0.0:
+  version "2.0.0"
+  resolved "https://registry.yarnpkg.com/to-fast-properties/-/to-fast-properties-2.0.0.tgz#dc5e698cbd079265bc73e0377681a4e4e83f616e"
+
 touch@^3.1.0:
   version "3.1.0"
   resolved "https://registry.yarnpkg.com/touch/-/touch-3.1.0.tgz#fe365f5f75ec9ed4e56825e0bb76d24ab74af83b"
@@ -4302,6 +4473,10 @@ unique-string@^1.0.0:
   dependencies:
     crypto-random-string "^1.0.0"
 
+universalify@^0.1.0:
+  version "0.1.1"
+  resolved "https://registry.yarnpkg.com/universalify/-/universalify-0.1.1.tgz#fa71badd4437af4c148841e3b3b165f9e9e590b7"
+
 unpipe@~1.0.0:
   version "1.0.0"
   resolved "https://registry.yarnpkg.com/unpipe/-/unpipe-1.0.0.tgz#b2bf4ee8514aae6165b4817829d21b2ef49904ec"
@@ -4481,6 +4656,12 @@ yallist@^2.1.2:
   version "2.1.2"
   resolved "https://registry.yarnpkg.com/yallist/-/yallist-2.1.2.tgz#1c11f9218f076089a47dd512f93c6699a6a81d52"
 
+yargs-parser@^7.0.0:
+  version "7.0.0"
+  resolved "https://registry.yarnpkg.com/yargs-parser/-/yargs-parser-7.0.0.tgz#8d0ac42f16ea55debd332caf4c4038b3e3f5dfd9"
+  dependencies:
+    camelcase "^4.1.0"
+
 yargs-parser@^8.0.0:
   version "8.1.0"
   resolved "https://registry.yarnpkg.com/yargs-parser/-/yargs-parser-8.1.0.tgz#f1376a33b6629a5d063782944da732631e966950"
@@ -4504,6 +4685,24 @@ yargs@^10.0.3:
     y18n "^3.2.1"
     yargs-parser "^8.0.0"
 
+yargs@^8.0.2:
+  version "8.0.2"
+  resolved "https://registry.yarnpkg.com/yargs/-/yargs-8.0.2.tgz#6299a9055b1cefc969ff7e79c1d918dceb22c360"
+  dependencies:
+    camelcase "^4.1.0"
+    cliui "^3.2.0"
+    decamelize "^1.1.1"
+    get-caller-file "^1.0.1"
+    os-locale "^2.0.0"
+    read-pkg-up "^2.0.0"
+    require-directory "^2.1.1"
+    require-main-filename "^1.0.1"
+    set-blocking "^2.0.0"
+    string-width "^2.0.0"
+    which-module "^2.0.0"
+    y18n "^3.2.1"
+    yargs-parser "^7.0.0"
+
 yargs@~3.10.0:
   version "3.10.0"
   resolved "https://registry.yarnpkg.com/yargs/-/yargs-3.10.0.tgz#f7ee7bd857dd7c1d2d38c0e74efbd681d1431fd1"