Three.js is a JavaScript 3D library, so all you need to create Three.js WebGL applications is a text editor and one of the supported web browsers to render the results. I would like to recommend the following JavaScript editors, which I've used extensively over the last couple of years on various projects:
Atom (text editor): is a free and open-source text and source code editor for macOS, Linux,
and Microsoft Windows with support for plug-ins written in Node.js, and embedded Git Control, developed by GitHub.
Atom is a desktop application built using web technologies.
Most of the extending packages have free software licenses and are community-built and maintained.
Atom is based on Electron (formerly known as Atom Shell), a framework that enables cross-platform desktop applications using Chromium and Node.js.
It is written in CoffeeScript and Less.
Atom was released from beta, as version 1.0, on 25 June 2015. Its developers call it a "hackable text editor for the 21st Century".
It is fully customizable in HTML, CSS, and JavaScript.
It can be downloaded the editor from
https://atom.io/
Visual Studio Code: This free editor from Microsoft runs on all major platforms and provides
great syntax highlighting and smart completion based on types, function definitions, and imported libraries.
It provides a very clean interface and is great for working on JavaScript projects.
It can be downloaded the editor from
https://code.visualstudio.com/
WebStorm: This editor from the JetBrains guys has great support for editing JavaScript.
It supports code completion, automatic deployment, and JavaScript debugging directly from the editor.
Besides this, WebStorm has excellent GitHub (and other version control systems) support.
You can download a trial edition from
https://www.jetbrains.com/webstorm/
Notepad++: Notepad++ is a general-purpose editor that supports code highlighting for a wide range of
programming languages. It can easily layout and format JavaScript. Note that Notepad++ is only for Windows.
You can download Notepad++ from
https://notepad-plus-plus.org/
Sublime Text Editor: Sublime is a great editor that offers very good support for editing
JavaScript. Besides this, it provides many very helpful selections (such as multiple-line select) and
edit options, which, once you get used to them, provide a really good JavaScript-editing environment.
Sublime can also be tested for free and can be downloaded from
http://www.sublimetext.com/