diff --git a/.eslintrc.json b/.eslintrc.json
new file mode 100644
index 0000000..f4cf0bb
--- /dev/null
+++ b/.eslintrc.json
@@ -0,0 +1,49 @@
+{
+  "extends": "eslint:recommended",
+  "parserOptions": {
+    "ecmaVersion": 8
+  },
+  "env": {
+    "es6": true,
+    "jest": true,
+    "node": true
+  },
+  "rules": {
+    "eol-last": "error",
+    "eqeqeq": [
+      "error",
+      "always"
+    ],
+    "indent": [
+      "error",
+      2
+    ],
+    "new-cap": "warn",
+    "no-console": "off",
+    "no-multi-spaces": [
+      "warn",
+      {
+        "exceptions": {
+          "VariableDeclarator": true
+        }
+      }
+    ],
+    "no-redeclare": [
+      "error",
+      {
+        "builtinGlobals": true
+      }
+    ],
+    "no-template-curly-in-string": "error",
+    "no-trailing-spaces": "warn",
+    "no-undefined": "off",
+    "quotes": [
+      "warn",
+      "single",
+      {
+        "allowTemplateLiterals": true
+      }
+    ],
+    "semi": "error"
+  }
+}
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..0235aaa
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,231 @@
+
+# Created by https://www.gitignore.io/api/node,macos,linux,windows,webstorm,visualstudiocode
+
+### Linux ###
+*~
+
+# temporary files which can be created if a process still has a handle open of a deleted file
+.fuse_hidden*
+
+# KDE directory preferences
+.directory
+
+# Linux trash folder which might appear on any partition or disk
+.Trash-*
+
+# .nfs files are created when an open file is removed but is still being accessed
+.nfs*
+
+### macOS ###
+# General
+.DS_Store
+.AppleDouble
+.LSOverride
+
+# Icon must end with two \r
+Icon
+
+# Thumbnails
+._*
+
+# Files that might appear in the root of a volume
+.DocumentRevisions-V100
+.fseventsd
+.Spotlight-V100
+.TemporaryItems
+.Trashes
+.VolumeIcon.icns
+.com.apple.timemachine.donotpresent
+
+# Directories potentially created on remote AFP share
+.AppleDB
+.AppleDesktop
+Network Trash Folder
+Temporary Items
+.apdisk
+
+### Node ###
+# Logs
+logs
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+
+# Runtime data
+pids
+*.pid
+*.seed
+*.pid.lock
+
+# Directory for instrumented libs generated by jscoverage/JSCover
+lib-cov
+
+# Coverage directory used by tools like istanbul
+coverage
+
+# nyc test coverage
+.nyc_output
+
+# Grunt intermediate storage (http://gruntjs.com/creating-plugins#storing-task-files)
+.grunt
+
+# Bower dependency directory (https://bower.io/)
+bower_components
+
+# node-waf configuration
+.lock-wscript
+
+# Compiled binary addons (https://nodejs.org/api/addons.html)
+build/Release
+
+# Dependency directories
+node_modules/
+jspm_packages/
+
+# TypeScript v1 declaration files
+typings/
+
+# Optional npm cache directory
+.npm
+
+# Optional eslint cache
+.eslintcache
+
+# Optional REPL history
+.node_repl_history
+
+# Output of 'npm pack'
+*.tgz
+
+# Yarn Integrity file
+.yarn-integrity
+
+# dotenv environment variables file
+.env
+
+# parcel-bundler cache (https://parceljs.org/)
+.cache
+
+# next.js build output
+.next
+
+# nuxt.js build output
+.nuxt
+
+# vuepress build output
+.vuepress/dist
+
+# Serverless directories
+.serverless
+
+### VisualStudioCode ###
+.vscode/*
+!.vscode/settings.json
+!.vscode/tasks.json
+!.vscode/launch.json
+!.vscode/extensions.json
+
+### WebStorm ###
+# Covers JetBrains IDEs: IntelliJ, RubyMine, PhpStorm, AppCode, PyCharm, CLion, Android Studio and WebStorm
+# Reference: https://intellij-support.jetbrains.com/hc/en-us/articles/206544839
+
+# User-specific stuff
+.idea/**/workspace.xml
+.idea/**/tasks.xml
+.idea/**/usage.statistics.xml
+.idea/**/dictionaries
+.idea/**/shelf
+
+# Sensitive or high-churn files
+.idea/**/dataSources/
+.idea/**/dataSources.ids
+.idea/**/dataSources.local.xml
+.idea/**/sqlDataSources.xml
+.idea/**/dynamic.xml
+.idea/**/uiDesigner.xml
+.idea/**/dbnavigator.xml
+
+# Gradle
+.idea/**/gradle.xml
+.idea/**/libraries
+
+# Gradle and Maven with auto-import
+# When using Gradle or Maven with auto-import, you should exclude module files,
+# since they will be recreated, and may cause churn.  Uncomment if using
+# auto-import.
+# .idea/modules.xml
+# .idea/*.iml
+# .idea/modules
+
+# CMake
+cmake-build-*/
+
+# Mongo Explorer plugin
+.idea/**/mongoSettings.xml
+
+# File-based project format
+*.iws
+
+# IntelliJ
+out/
+
+# mpeltonen/sbt-idea plugin
+.idea_modules/
+
+# JIRA plugin
+atlassian-ide-plugin.xml
+
+# Cursive Clojure plugin
+.idea/replstate.xml
+
+# Crashlytics plugin (for Android Studio and IntelliJ)
+com_crashlytics_export_strings.xml
+crashlytics.properties
+crashlytics-build.properties
+fabric.properties
+
+# Editor-based Rest Client
+.idea/httpRequests
+
+### WebStorm Patch ###
+# Comment Reason: https://github.com/joeblau/gitignore.io/issues/186#issuecomment-215987721
+
+# *.iml
+# modules.xml
+# .idea/misc.xml
+# *.ipr
+
+# Sonarlint plugin
+.idea/sonarlint
+
+### Windows ###
+# Windows thumbnail cache files
+Thumbs.db
+ehthumbs.db
+ehthumbs_vista.db
+
+# Dump file
+*.stackdump
+
+# Folder config file
+[Dd]esktop.ini
+
+# Recycle Bin used on file shares
+$RECYCLE.BIN/
+
+# Windows Installer files
+*.cab
+*.msi
+*.msix
+*.msm
+*.msp
+
+# Windows shortcuts
+*.lnk
+
+# Visual Studio 2015/2017 cache/options directory
+.vs/
+
+
+# End of https://www.gitignore.io/api/node,macos,linux,windows,webstorm,visualstudiocode
diff --git a/.markdownlint.json b/.markdownlint.json
new file mode 100644
index 0000000..e11c946
--- /dev/null
+++ b/.markdownlint.json
@@ -0,0 +1,15 @@
+{
+  "line-length": false,
+  "no-trailing-punctuation": false,
+  "no-inline-html": {
+    "allowed_elements": [
+      "a",
+      "dl",
+      "dt",
+      "dd",
+      "summary",
+      "detail",
+      "img"
+    ]
+  }
+}
diff --git a/class-15/.DS_Store b/class-15/.DS_Store
index fa58f16..4704268 100644
Binary files a/class-15/.DS_Store and b/class-15/.DS_Store differ