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1.4The REPL
A REPL (Read-Eval-Print Loop) lets you type code interactively and see results immediately. Use it to experiment.
# Python REPL
python
>>> 2 + 2
4
>>> "test" + "_login"
'test_login'
>>> exit()
# Node.js REPL (works for both JS and quick TS experiments)
node
> 2 + 2
4
> "test" + "_login"
'test_login'
> .exit
TypeScript does not ship a built-in REPL, but npx tsx can run .ts files instantly. For interactive exploration, use the Node REPL and add types when you move code into a .ts file.