ESLint : The pluggable linting utility for JavaScript and JSX
Flume : A React-powered node editor and runtime engine. Build apps that are resilient to changing requirements by modeling your business logic as a JSON graph...
JSHint : A JavaScript Code Quality Tool. JSHint is a tool that helps to detect errors and potential problems in your JavaScript code.
DOM Monster Bookmarklet : DOM Monster is a cross-platform, cross-browser bookmarklet that will analyze the DOM & other features of the page you're on, and give you its bill of ...
A toolkit for React, Preact & Inferno apps, React libraries and other npm modules for the web, with no configuration (until you need it)