In which functional programming languages have you worked or applied in your projects?

In Node.js projects, functional languages or paradigms are often used, for example:

• JavaScript itself supports a functional style: first-class functions, closures, higher-order functions.
• Using libraries such as Ramda or Lodash/fp, which provide convenient functional utilities.
• Sometimes languages that compile to JavaScript are used, such as TypeScript with functional patterns, or Elm, PureScript, which are strictly functional.

The functional approach helps write clean, predictable code with fewer side effects, which is especially useful in asynchronous applications on Node.js.