diff --git a/.eslintrc b/.eslintrc
index 5103e0e..a3bad8a 100644
--- a/.eslintrc
+++ b/.eslintrc
@@ -3,11 +3,13 @@
   "env": {
     "browser": true,
     "node": true,
-    "mocha": true
+    "mocha": true,
+    "worker": true
   },
   "rules": {
     "no-underscore-dangle": 0,
     "no-console": 0,
-    "global-require": 0
+    "global-require": 0,
+    "camelcase": 0
   }
 }
diff --git a/package-lock.json b/package-lock.json
index 3b5029b..b515578 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -381,6 +381,12 @@
         "negotiator": "0.6.1"
       }
     },
+    "acorn": {
+      "version": "6.1.1",
+      "resolved": "https://registry.npmjs.org/acorn/-/acorn-6.1.1.tgz",
+      "integrity": "sha512-jPTiwtOxaHNaAPg/dmrJ/beuzLRnXtB0kQPQ8JpotKJgTB6rX6c8mlf315941pyjBSaPg8NHXS9fhP4u17DpGA==",
+      "dev": true
+    },
     "acorn-dynamic-import": {
       "version": "3.0.0",
       "resolved": "https://registry.npmjs.org/acorn-dynamic-import/-/acorn-dynamic-import-3.0.0.tgz",
@@ -2549,14 +2555,12 @@
         "balanced-match": {
           "version": "1.0.0",
           "bundled": true,
-          "dev": true,
-          "optional": true
+          "dev": true
         },
         "brace-expansion": {
           "version": "1.1.11",
           "bundled": true,
           "dev": true,
-          "optional": true,
           "requires": {
             "balanced-match": "^1.0.0",
             "concat-map": "0.0.1"
@@ -2571,20 +2575,17 @@
         "code-point-at": {
           "version": "1.1.0",
           "bundled": true,
-          "dev": true,
-          "optional": true
+          "dev": true
         },
         "concat-map": {
           "version": "0.0.1",
           "bundled": true,
-          "dev": true,
-          "optional": true
+          "dev": true
         },
         "console-control-strings": {
           "version": "1.1.0",
           "bundled": true,
-          "dev": true,
-          "optional": true
+          "dev": true
         },
         "core-util-is": {
           "version": "1.0.2",
@@ -2701,8 +2702,7 @@
         "inherits": {
           "version": "2.0.3",
           "bundled": true,
-          "dev": true,
-          "optional": true
+          "dev": true
         },
         "ini": {
           "version": "1.3.5",
@@ -2714,7 +2714,6 @@
           "version": "1.0.0",
           "bundled": true,
           "dev": true,
-          "optional": true,
           "requires": {
             "number-is-nan": "^1.0.0"
           }
@@ -2729,7 +2728,6 @@
           "version": "3.0.4",
           "bundled": true,
           "dev": true,
-          "optional": true,
           "requires": {
             "brace-expansion": "^1.1.7"
           }
@@ -2737,14 +2735,12 @@
         "minimist": {
           "version": "0.0.8",
           "bundled": true,
-          "dev": true,
-          "optional": true
+          "dev": true
         },
         "minipass": {
           "version": "2.2.4",
           "bundled": true,
           "dev": true,
-          "optional": true,
           "requires": {
             "safe-buffer": "^5.1.1",
             "yallist": "^3.0.0"
@@ -2763,7 +2759,6 @@
           "version": "0.5.1",
           "bundled": true,
           "dev": true,
-          "optional": true,
           "requires": {
             "minimist": "0.0.8"
           }
@@ -2844,8 +2839,7 @@
         "number-is-nan": {
           "version": "1.0.1",
           "bundled": true,
-          "dev": true,
-          "optional": true
+          "dev": true
         },
         "object-assign": {
           "version": "4.1.1",
@@ -2857,7 +2851,6 @@
           "version": "1.4.0",
           "bundled": true,
           "dev": true,
-          "optional": true,
           "requires": {
             "wrappy": "1"
           }
@@ -2979,7 +2972,6 @@
           "version": "1.0.2",
           "bundled": true,
           "dev": true,
-          "optional": true,
           "requires": {
             "code-point-at": "^1.0.0",
             "is-fullwidth-code-point": "^1.0.0",
diff --git a/package.json b/package.json
index 80a3cd0..7f266be 100644
--- a/package.json
+++ b/package.json
@@ -25,6 +25,7 @@
   ],
   "license": "Apache-2.0",
   "devDependencies": {
+    "acorn": "^6.1.1",
     "cors": "^2.8.5",
     "eslint": "^5.9.0",
     "eslint-config-airbnb": "^17.1.0",
diff --git a/src/browser/index.js b/src/browser/index.js
index 28b36df..8568171 100644
--- a/src/browser/index.js
+++ b/src/browser/index.js
@@ -39,7 +39,7 @@ const readFromBlobOrFile = (blob, res) => {
  *   string: URL string, can be relative path
  *   img HTMLElement: extract image source from src attribute
  *   video HTMLElement: extract image source from poster attribute
- *   canvas HTMLElement: extract image data by converting to Blob 
+ *   canvas HTMLElement: extract image data by converting to Blob
  *   File instance: data from <input type="file" />
  * @returns {array} binary image in array format
  */
@@ -88,7 +88,7 @@ const downloadFile = (path, blob) => {
       document.body.removeChild(link);
     }
   }
-}
+};
 
 /*
  * Default options for browser worker
diff --git a/src/browser/worker.js b/src/browser/worker.js
index 3a2b092..55a6cbe 100644
--- a/src/browser/worker.js
+++ b/src/browser/worker.js
@@ -33,7 +33,7 @@ workerUtils.setAdapter({
        */
       if (check.not.undefined(global.TesseractCoreWASM) && typeof WebAssembly === 'object') {
         global.TesseractCore = global.TesseractCoreWASM;
-      } else if (check.not.undefined(global.TesseractCoreASM)){
+      } else if (check.not.undefined(global.TesseractCoreASM)) {
         global.TesseractCore = global.TesseractCoreASM;
       } else {
         throw Error('Failed to load TesseractCore');
@@ -44,7 +44,7 @@ workerUtils.setAdapter({
   },
   b64toU8Array: s => new Uint8Array(atob(s).split('').map(c => c.charCodeAt(0))),
   writeFile: (path, data, type) => {
-    self.postMessage({
+    postMessage({
       jobId: 'Download',
       path,
       data,
diff --git a/src/common/workerUtils.js b/src/common/workerUtils.js
index 0aa434e..a26c2dc 100644
--- a/src/common/workerUtils.js
+++ b/src/common/workerUtils.js
@@ -8,7 +8,6 @@
  * @author Jerome Wu <jeromewus@gmail.com>
  */
 const { readImage, loadLang } = require('tesseract.js-utils');
-const check = require('check-types');
 const pdfTTF = require('./pdf-ttf');
 const dump = require('./dump');
 const { defaultParams } = require('./options');
@@ -59,7 +58,7 @@ const setImage = (image) => {
  * @name handleParams
  * @function hanlde params from users
  * @access private
- * @param {string} lang - lang string for Init() 
+ * @param {string} lang - lang string for Init()
  * @param {object} customParams - an object of params
  */
 const handleParams = (lang, customParams) => {
@@ -110,14 +109,14 @@ const handleOutput = (customParams) => {
     if (pdf_bin) {
       files = { pdf: data, ...files };
     }
-    
+
     if (pdf_auto_download) {
       adapter.writeFile(`${pdf_name}.pdf`, data, 'application/pdf');
     }
   }
 
   return files;
-}
+};
 
 /**
  * handleInit