A JavaScript online compiler and a local development environment differ in several ways. Here are some key differences:

1. Accessibility: An online compiler is accessed through a web browser, making it easily accessible from any device with an internet connection. On the other hand, a local development environment requires installation and setup on the user's computer.

2. Setup and Configuration: Online compilers do not require any installation or configuration since they are already set up on the online platform. In contrast, a local development environment typically requires the installation of specific software, such as a code editor, a JavaScript runtime, and possibly additional libraries or frameworks.

3. Resources and Dependencies: Online compilers are hosted on remote servers, which means they provide their own resources and dependencies. This can be advantageous as it eliminates the need to manage dependencies and ensures consistent behavior across different devices. In a local development environment, the user is responsible for managing resources, installing dependencies, and configuring the environment as needed.

4. Collaboration: Online compilers often offer collaborative features that enable multiple users to work on the same code simultaneously. This can be useful for pair programming or team collaborations. Local development environments generally require additional tools or configurations for collaborative coding.

5. Offline Usage: Online compilers rely on an internet connection to function, so they may not be accessible when offline. Conversely, a local development environment allows you to work on your code even without an internet connection.

6. Flexibility and Customization: Local development environments provide more flexibility and customization options. You can choose your preferred code editor, customize the development environment to fit your specific needs, and integrate additional tools or extensions. Online compilers usually have predefined settings and limited customization options.

It's important to note that both online compilers and local development environments have their own advantages and use cases. The choice between them depends on factors such as your development workflow, collaboration requirements, the need for customization, and accessibility preferences.