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
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