Download from: http://nodejs.org/ Node.js. Run as node. Ctrl-C (twice) to quit.

On Ubuntu I had to install the nodejs package and the command is called nodejs as there was already command called node.

On Mac first install Homebrew http://mxcl.github.io/homebrew/ and then brew install node.

Maybe you'll need to use the Git bash shell...

> .help
> .exit

> .break

Some JavaScript using the Node.js REPL

Variables and numbers

> a = 23
23
> b = 19
19
> a+b
42

The behaviour of + depends on the operands. If even one of them is a sting, + will concatenate them as string. Use parseInt() to convert a string to an integer.

> c = "1"
> a+c
'231'
> a+parseInt(c)
24