Starting a REPL

Node can be used as a terminal command-line interface where javascript can be written into a terminal. This can be started by writing into a terminal

node # then press "return"

The output will look something like

$ node
Welcome to Node.js v16.some.sub.version
Type ".help" for more information.
> 

Notice the >, which is the repl that accepts js. For those coming from a frontend-focused environment, this repl space might feel something like a js "playground". JS can be written and quickly inspected. Try something like...

> const horse = 'cat';
undefined

> horse //return
'cat'

> 2 + 2
4

> const a = { one: 'first key', two: 'second key'}
undefined 

> a.two
'second key'

> Object.keys(a).forEach((k,idx) => console.log(`Key of ${k} is at idx ${idx}`))
 Key of one is at idx 0
Key of two is at idx 1
undefined

This REPL can even store things like functions to run "later":

// copy & paste this into the repl and press "return"
> function add(a, b) { return a + b }
undefined

// Then try using this function
> add(2,3)
5

To "cancel" and escape out of this node repl and return to the machine's "native" terminal environment, I've always pressed Ctrl + C 2x. The first time pressing Ctrl + C node even prints a message,

(To exit, press Ctrl+C again or Ctrl+D or type .exit)