diff --git a/lib/application.js b/lib/application.js
index b19055ec82..797069d700 100644
--- a/lib/application.js
+++ b/lib/application.js
@@ -297,12 +297,10 @@ app.engine = function engine(ext, fn) {
     throw new Error('callback function required');
   }
 
-  // get file extension
-  var extension = ext[0] !== '.'
-    ? '.' + ext
-    : ext;
+  // Get file extension
+  const extension = ext.startsWith('.') ? ext : `.${ext}`;
 
-  // store engine
+  // Store engine function
   this.engines[extension] = fn;
 
   return this;
diff --git a/lib/request.js b/lib/request.js
index 372a9915e9..063f88a236 100644
--- a/lib/request.js
+++ b/lib/request.js
@@ -255,16 +255,7 @@ defineGetter(req, 'query', function query(){
  */
 
 req.is = function is(types) {
-  var arr = types;
-
-  // support flattened arguments
-  if (!Array.isArray(types)) {
-    arr = new Array(arguments.length);
-    for (var i = 0; i < arr.length; i++) {
-      arr[i] = arguments[i];
-    }
-  }
-
+  const arr = Array.isArray(types) ? types : Array.from(arguments);
   return typeis(this, arr);
 };
 
diff --git a/lib/utils.js b/lib/utils.js
index 67eacf274e..bb40c78cd7 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -50,10 +50,10 @@ exports.wetag = createETagGenerator({ weak: true })
  * @api private
  */
 
-exports.normalizeType = function(type){
-  return ~type.indexOf('/')
+exports.normalizeType = function(type) {
+  return type.includes('/')
     ? acceptParams(type)
-    : { value: (mime.lookup(type) || 'application/octet-stream'), params: {} }
+    : { value: mime.lookup(type) || 'application/octet-stream', params: {} };
 };
 
 /**
@@ -64,15 +64,16 @@ exports.normalizeType = function(type){
  * @api private
  */
 
-exports.normalizeTypes = function(types){
-  var ret = [];
+exports.normalizeTypes = function(types) {
+  const len = types.length;
+  const ret = new Array(len);
 
-  for (var i = 0; i < types.length; ++i) {
-    ret.push(exports.normalizeType(types[i]));
+  for (let i = 0; i < len; i++) {
+    ret[i] = exports.normalizeType(types[i]);
   }
 
   return ret;
-};
+}
 
 /**
  * Parse accept params `str` returning an
@@ -83,16 +84,16 @@ exports.normalizeTypes = function(types){
  * @api private
  */
 
-function acceptParams (str) {
-  var parts = str.split(/ *; */);
-  var ret = { value: parts[0], quality: 1, params: {} }
+function acceptParams(str) {
+  const parts = str.split(/ *; */);
+  const ret = { value: parts[0], quality: 1, params: {} };
 
-  for (var i = 1; i < parts.length; ++i) {
-    var pms = parts[i].split(/ *= */);
-    if ('q' === pms[0]) {
-      ret.quality = parseFloat(pms[1]);
+  for (let i = 1; i < parts.length; i++) {
+    const [key, value] = parts[i].split(/ *= */);
+    if (key === 'q') {
+      ret.quality = parseFloat(value);
     } else {
-      ret.params[pms[0]] = pms[1];
+      ret.params[key] = value;
     }
   }
 
@@ -108,27 +109,23 @@ function acceptParams (str) {
  */
 
 exports.compileETag = function(val) {
-  var fn;
-
   if (typeof val === 'function') {
     return val;
   }
 
+  if (val === false) {
+    return;
+  }
+
   switch (val) {
     case true:
     case 'weak':
-      fn = exports.wetag;
-      break;
-    case false:
-      break;
+      return exports.wetag;
     case 'strong':
-      fn = exports.etag;
-      break;
+      return exports.etag;
     default:
-      throw new TypeError('unknown value for etag function: ' + val);
+      throw new TypeError(`unknown value for etag function: ${val}`);
   }
-
-  return fn;
 }
 
 /**
@@ -139,28 +136,24 @@ exports.compileETag = function(val) {
  * @api private
  */
 
-exports.compileQueryParser = function compileQueryParser(val) {
-  var fn;
-
+exports.compileQueryParser = function (val) {
   if (typeof val === 'function') {
     return val;
   }
 
+  if (val === false) {
+    return;
+  }
+
   switch (val) {
     case true:
     case 'simple':
-      fn = querystring.parse;
-      break;
-    case false:
-      break;
+      return querystring.parse;
     case 'extended':
-      fn = parseExtendedQueryString;
-      break;
+      return parseExtendedQueryString;
     default:
-      throw new TypeError('unknown value for query parser function: ' + val);
+      throw new TypeError(`unknown value for query parser function: ${val}`);
   }
-
-  return fn;
 }
 
 /**
@@ -226,16 +219,16 @@ exports.setCharset = function setCharset(type, charset) {
  * @private
  */
 
-function createETagGenerator (options) {
-  return function generateETag (body, encoding) {
-    var buf = !Buffer.isBuffer(body)
-      ? Buffer.from(body, encoding)
-      : body
-
-    return etag(buf, options)
-  }
+function createETagGenerator(options) {
+  return (body, encoding) => {
+    const buf = Buffer.isBuffer(body)
+      ? body
+      : Buffer.from(body, encoding);
+    return etag(buf, options);
+  };
 }
 
+
 /**
  * Parse an extended query string with qs.
  *
diff --git a/lib/view.js b/lib/view.js
index 6beffca6e2..383bd00667 100644
--- a/lib/view.js
+++ b/lib/view.js
@@ -167,23 +167,17 @@ View.prototype.render = function render(options, callback) {
  */
 
 View.prototype.resolve = function resolve(dir, file) {
-  var ext = this.ext;
+  const ext = this.ext;
 
-  // <path>.<ext>
-  var path = join(dir, file);
-  var stat = tryStat(path);
+  // Check <path>.<ext>
+  let path = join(dir, file);
+  if (tryStat(path)?.isFile()) return path;
 
-  if (stat && stat.isFile()) {
-    return path;
-  }
-
-  // <path>/index.<ext>
-  path = join(dir, basename(file, ext), 'index' + ext);
-  stat = tryStat(path);
+  // Check <path>/index.<ext>
+  path = join(dir, basename(file, ext), `index${ext}`);
+  if (tryStat(path)?.isFile()) return path;
 
-  if (stat && stat.isFile()) {
-    return path;
-  }
+  return undefined;
 };
 
 /**
@@ -195,11 +189,10 @@ View.prototype.resolve = function resolve(dir, file) {
  */
 
 function tryStat(path) {
-  debug('stat "%s"', path);
-
+  debug(`stat "${path}"`);
   try {
     return fs.statSync(path);
-  } catch (e) {
+  } catch {
     return undefined;
   }
 }