diff --git a/.eslintrc b/.eslintrc
index 6bebcd2..9d817ff 100644
--- a/.eslintrc
+++ b/.eslintrc
@@ -4,9 +4,17 @@ env:
   mocha: true
   node: true
 
+extends: "airbnb-base"
+
+parserOptions:
+  sourceType: "script"
+
 rules:
   max-len:
     - 2
     - 120
-
-extends: "airbnb-base"
+  no-multi-assign: "off"
+  no-param-reassign: "off"
+  strict:
+    - "error"
+    - "safe"
diff --git a/index.js b/index.js
index 3d03cea..3d98e70 100644
--- a/index.js
+++ b/index.js
@@ -1,3 +1,5 @@
+'use strict';
+
 const path = require('path');
 const chalk = require('chalk');
 const PluginError = require('plugin-error');
@@ -9,151 +11,161 @@ const applySourceMap = require('vinyl-sourcemaps-apply');
 
 const PLUGIN_NAME = 'gulp-sass';
 
-/// ///////////////////////////
-// Main Gulp Sass function
-/// ///////////////////////////
-const gulpSass = (options, sync) => transfob((file, enc, cb) => { // eslint-disable-line consistent-return
-  if (file.isNull()) {
-    return cb(null, file);
-  }
+const MISSING_COMPILER_MESSAGE = `
+gulp-sass 5 does not have a default Sass compiler; please set one yourself.
+Both the "sass" and "node-sass" packages are permitted.
+For example, in your gulpfile:
+
+  const sass = require('gulp-sass')(require('sass'));
+`;
+
+/**
+ * Handles returning the file to the stream
+ */
+const filePush = (file, sassObject, callback) => {
+  // Build Source Maps!
+  if (sassObject.map) {
+    // Transform map into JSON
+    const sassMap = JSON.parse(sassObject.map.toString());
+    // Grab the stdout and transform it into stdin
+    const sassMapFile = sassMap.file.replace(/^stdout$/, 'stdin');
+    // Grab the base filename that's being worked on
+    const sassFileSrc = file.relative;
+    // Grab the path portion of the file that's being worked on
+    const sassFileSrcPath = path.dirname(sassFileSrc);
+
+    if (sassFileSrcPath) {
+      const sourceFileIndex = sassMap.sources.indexOf(sassMapFile);
+      // Prepend the path to all files in the sources array except the file that's being worked on
+      sassMap.sources = sassMap.sources.map((source, index) => (
+        index === sourceFileIndex
+          ? source
+          : path.join(sassFileSrcPath, source)
+      ));
+    }
 
-  if (file.isStream()) {
-    return cb(new PluginError(PLUGIN_NAME, 'Streaming not supported'));
-  }
+    // Remove 'stdin' from souces and replace with filenames!
+    sassMap.sources = sassMap.sources.filter((src) => src !== 'stdin' && src);
 
-  if (path.basename(file.path).startsWith('_')) {
-    return cb();
+    // Replace the map file with the original filename (but new extension)
+    sassMap.file = replaceExtension(sassFileSrc, '.css');
+    // Apply the map
+    applySourceMap(file, sassMap);
   }
 
-  if (!file.contents.length) {
-    file.path = replaceExtension(file.path, '.css'); // eslint-disable-line no-param-reassign
-    return cb(null, file);
+  file.contents = sassObject.css;
+  file.path = replaceExtension(file.path, '.css');
+
+  if (file.stat) {
+    file.stat.atime = file.stat.mtime = file.stat.ctime = new Date();
   }
 
-  const opts = clonedeep(options || {});
-  opts.data = file.contents.toString();
+  callback(null, file);
+};
+
+/**
+ * Handles error message
+ */
+const handleError = (error, file, callback) => {
+  const filePath = (error.file === 'stdin' ? file.path : error.file) || file.path;
+  const relativePath = path.relative(process.cwd(), filePath);
+  const message = [chalk.underline(relativePath), error.formatted].join('\n');
 
-  // we set the file path here so that libsass can correctly resolve import paths
-  opts.file = file.path;
+  error.messageFormatted = message;
+  error.messageOriginal = error.message;
+  error.message = stripAnsi(message);
+  error.relativePath = relativePath;
 
-  // Ensure `indentedSyntax` is true if a `.sass` file
-  if (path.extname(file.path) === '.sass') {
-    opts.indentedSyntax = true;
-  }
+  return callback(new PluginError(PLUGIN_NAME, error));
+};
 
-  // Ensure file's parent directory in the include path
-  if (opts.includePaths) {
-    if (typeof opts.includePaths === 'string') {
-      opts.includePaths = [opts.includePaths];
+/**
+ * Main Gulp Sass function
+ */
+
+// eslint-disable-next-line arrow-body-style
+const gulpSass = (options, sync) => {
+  // eslint-disable-next-line consistent-return
+  return transfob((file, encoding, callback) => {
+    if (file.isNull()) {
+      return callback(null, file);
+    }
+
+    if (file.isStream()) {
+      return callback(new PluginError(PLUGIN_NAME, 'Streaming not supported'));
     }
-  } else {
-    opts.includePaths = [];
-  }
 
-  opts.includePaths.unshift(path.dirname(file.path));
+    if (path.basename(file.path).startsWith('_')) {
+      return callback();
+    }
 
-  // Generate Source Maps if plugin source-map present
-  if (file.sourceMap) {
-    opts.sourceMap = file.path;
-    opts.omitSourceMapUrl = true;
-    opts.sourceMapContents = true;
-  }
+    if (!file.contents.length) {
+      file.path = replaceExtension(file.path, '.css');
+      return callback(null, file);
+    }
 
-  /// ///////////////////////////
-  // Handles returning the file to the stream
-  /// ///////////////////////////
-  const filePush = (sassObj) => {
-    let sassMap;
-    let sassMapFile;
-    let sassFileSrc;
-    let sassFileSrcPath;
-    let sourceFileIndex;
-
-    // Build Source Maps!
-    if (sassObj.map) {
-      // Transform map into JSON
-      sassMap = JSON.parse(sassObj.map.toString());
-      // Grab the stdout and transform it into stdin
-      sassMapFile = sassMap.file.replace(/^stdout$/, 'stdin');
-      // Grab the base file name that's being worked on
-      sassFileSrc = file.relative;
-      // Grab the path portion of the file that's being worked on
-      sassFileSrcPath = path.dirname(sassFileSrc);
-      if (sassFileSrcPath) {
-        // Prepend the path to all files in the sources array except the file that's being worked on
-        sourceFileIndex = sassMap.sources.indexOf(sassMapFile);
-        sassMap.sources = sassMap.sources.map((source, index) => { // eslint-disable-line arrow-body-style
-          return index === sourceFileIndex ? source : path.join(sassFileSrcPath, source);
-        });
-      }
+    const opts = clonedeep(options || {});
+    opts.data = file.contents.toString();
+
+    // We set the file path here so that libsass can correctly resolve import paths
+    opts.file = file.path;
 
-      // Remove 'stdin' from souces and replace with filenames!
-      sassMap.sources = sassMap.sources.filter((src) => src !== 'stdin' && src);
+    // Ensure `indentedSyntax` is true if a `.sass` file
+    if (path.extname(file.path) === '.sass') {
+      opts.indentedSyntax = true;
+    }
 
-      // Replace the map file with the original file name (but new extension)
-      sassMap.file = replaceExtension(sassFileSrc, '.css');
-      // Apply the map
-      applySourceMap(file, sassMap);
+    // Ensure file's parent directory in the include path
+    if (opts.includePaths) {
+      if (typeof opts.includePaths === 'string') {
+        opts.includePaths = [opts.includePaths];
+      }
+    } else {
+      opts.includePaths = [];
     }
 
-    file.contents = sassObj.css; // eslint-disable-line no-param-reassign
-    file.path = replaceExtension(file.path, '.css'); // eslint-disable-line no-param-reassign
+    opts.includePaths.unshift(path.dirname(file.path));
 
-    if (file.stat) {
-      file.stat.atime = file.stat.mtime = file.stat.ctime = new Date(); // eslint-disable-line
+    // Generate Source Maps if the source-map plugin is present
+    if (file.sourceMap) {
+      opts.sourceMap = file.path;
+      opts.omitSourceMapUrl = true;
+      opts.sourceMapContents = true;
     }
 
-    cb(null, file);
-  };
-
-  /// ///////////////////////////
-  // Handles error message
-  /// ///////////////////////////
-  const errorM = (error) => {
-    const filePath = (error.file === 'stdin' ? file.path : error.file) || file.path;
-    const relativePath = path.relative(process.cwd(), filePath);
-    const message = [chalk.underline(relativePath), error.formatted].join('\n');
-
-    error.messageFormatted = message; // eslint-disable-line no-param-reassign
-    error.messageOriginal = error.message; // eslint-disable-line no-param-reassign
-    error.message = stripAnsi(message); // eslint-disable-line no-param-reassign
-    error.relativePath = relativePath; // eslint-disable-line no-param-reassign
-
-    return cb(new PluginError(PLUGIN_NAME, error));
-  };
-
-  if (sync !== true) {
-    /// ///////////////////////////
-    // Async Sass render
-    /// ///////////////////////////
-    const callback = (error, obj) => { // eslint-disable-line consistent-return
-      if (error) {
-        return errorM(error);
+    if (sync !== true) {
+      /**
+       * Async Sass render
+       */
+      // eslint-disable-next-line consistent-return
+      gulpSass.compiler.render(opts, (error, obj) => {
+        if (error) {
+          return handleError(error, file, callback);
+        }
+
+        filePush(file, obj, callback);
+      });
+    } else {
+      /**
+       * Sync Sass render
+       */
+      try {
+        filePush(file, gulpSass.compiler.renderSync(opts), callback);
+      } catch (error) {
+        return handleError(error, file, callback);
       }
-      filePush(obj);
-    };
-
-    gulpSass.compiler.render(opts, callback);
-  } else {
-    /// ///////////////////////////
-    // Sync Sass render
-    /// ///////////////////////////
-    try {
-      filePush(gulpSass.compiler.renderSync(opts));
-    } catch (error) {
-      return errorM(error);
     }
-  }
-});
+  });
+};
 
-/// ///////////////////////////
-// Sync Sass render
-/// ///////////////////////////
+/**
+ * Sync Sass render
+ */
 gulpSass.sync = (options) => gulpSass(options, true);
 
-/// ///////////////////////////
-// Log errors nicely
-/// ///////////////////////////
+/**
+ * Log errors nicely
+ */
 gulpSass.logError = function logError(error) {
   const message = new PluginError('sass', error.messageFormatted).toString();
   process.stderr.write(`${message}\n`);
@@ -164,17 +176,13 @@ module.exports = (compiler) => {
   if (!compiler || !compiler.render) {
     const message = new PluginError(
       PLUGIN_NAME,
-      '\n'
-      + 'gulp-sass 5 does not have a default Sass compiler; please set one yourself.\n'
-      + 'Both the `sass` and `node-sass` packages are permitted.\n'
-
-        + 'For example, in your gulpfile:\n\n'
-        + '  var sass = require(\'gulp-sass\')(require(\'sass\'));\n',
+      MISSING_COMPILER_MESSAGE,
       { showProperties: false },
     ).toString();
     process.stderr.write(`${message}\n`);
     process.exit(1);
   }
+
   gulpSass.compiler = compiler;
   return gulpSass;
 };
diff --git a/test/main.js b/test/main.js
index 284f119..5cd8bb1 100644
--- a/test/main.js
+++ b/test/main.js
@@ -1,3 +1,5 @@
+'use strict';
+
 const fs = require('fs');
 const path = require('path');
 const should = require('should');