What's a REPL?

A REPL stands for Read-Eval-Print Loop. It’s an interactive programming environment that:

1. Reads your input (code you type)
2. Evaluates it (runs the code)
3. Prints the result
4. Loops back to wait for more input

Think of it like a calculator, but for code! You can type in programming statements one at a time and see the results immediately, rather than having to write a whole program file and run it.

Common examples:

• Python’s interactive shell (when you just type python in terminal)
• jshell for Java
• JavaScript console in your browser (F12 → Console tab)
• Node.js command line
• Ruby’s irb (Interactive Ruby)

Why REPLs are useful:

• Testing small code snippets quickly
• Learning and experimenting with a language
• Debugging and exploring data
• Doing quick calculations or data analysis

So when I mentioned “analysis tool” earlier, that’s essentially a JavaScript REPL running in the browser - a place where you can write and run JavaScript code interactively to analyze data, do calculations, or test ideas without having to set up a full development environment.

It’s super handy for trying things out before writing them into a proper program!