To develop JavaScript applications, you need a JavaScript environment where you can write, test, and run your code. There are several ways to set up a JavaScript environment, depending on your needs and preferences. Here are a few options:

1. Using a web browser: You can write and test JavaScript code directly in your web browser's developer console. To access the console, open your browser and press F12 (or Ctrl + Shift + I on Windows/Linux or Cmd + Option + I on Mac) to open the Developer Tools. In the console tab, you can write JavaScript code and see the output. This is a great option for quick experiments or testing small code snippets.

2. Using a text editor: You can write JavaScript code in a text editor like VS Code, Sublime Text, or Atom. These editors have built-in support for syntax highlighting, code completion, and debugging, making it easier to write and test code. To run your code, you can use a tool like Node.js or a web browser.

3. Using an integrated development environment (IDE): An IDE like WebStorm, Visual Studio, or Eclipse provides a full-featured development environment for JavaScript applications. It includes tools for writing, testing, debugging, and deploying code, as well as support for version control and project management.

4. Using an online code editor: There are several online code editors like CodePen, JSFiddle, and Repl.it that allow you to write and test JavaScript code directly in your web browser. These editors provide a convenient way to share code and collaborate with others.

Once you have set up your JavaScript environment, you can start writing JavaScript code. To create a basic JavaScript program, you can write your code in a .js file and then run it using a tool like Node.js.