What scripting language works natively inside of nearly all modern Web browsers and may also...

Browser Ubiquity: JavaScript has a native runtime environment within almost every modern web browser, making it the 'built-in' scripting language for web-based interfaces.

Node-RED: This IoT flow-based programming tool specifically uses JavaScript for its logic and automation functions.

Other Languages:

PHP: Primarily server-side for web applications

Python: Versatile language, used in some back-end IoT functions but not natively in browsers

R: Statistical and data analysis, not typically embedded in wireless solutions

References:

JavaScript (Browser Compatibility): Documentation of its near-universal support

Node-RED (Programming Model): Descriptions of how it uses JavaScript for node logic.