My next challenge is to figure out how to make sure our node script is running on boot of the raspberry pi.

Simplified Script
This is our simplified script we want to run at system boot.

var wpi = require('wiring-pi');

var express = require('express');
var app = express();

wpi.wiringPiSetup();
var relaySwitchOne = 0;
wpi.pinMode(relaySwitchOne, wpi.OUTPUT);

app.get('/status', function(req, res){
    var result = !+ wpi.digitalRead(relaySwitchOne);
    res.send(''+ result);
});
app.get('/on', function (req, res) {
    wpi.digitalWrite(relaySwitchOne, 0);
    res.send('on');
});

app.get('/off', function(req, res){
    off();
    res.send('off');
});

function off(){
    wpi.digitalWrite(relaySwitchOne, 1);
}

var server = app.listen(3000, function () {
    var host = server.address().address;
    var port = server.address().port;

    console.log('Example app listening at http://%s:%s', host, port);
});

running it
After a bit of searching online I located foreverjs which seems very promising.

A simple CLI tool for ensuring that a given script runs continuously (i.e. forever).

Using sudo forever start index.js I could see the express server startup. This would allow the script to run forever, but what about on reboot. Additional searching I was brought to another question/answer that directs me to using forever-service. Looking at the docs I was able to execute the command sudo forever-service install pi-switch --script index.js which did its magic.

Commands to interact with service pi-switch
Start - "sudo service pi-switch start"
Stop - "sudo service pi-switch stop"
Status - "sudo service pi-switch status"
Restart - "sudo service pi-switch restart"

reboot
I rebooted the pi and the relay switched on (success) and running curl shows the express server is up. Double Success!

mental recap

• There is a library or package to do anything
• This package is doing some magic and it might be better to understand the higher upvoted answer as well.