Change text file when Raspberry Pi loses power - node.js

Question

I'm writing a small application for my Raspberry Pi to surveil my surroundings and I want to know when the Raspberry Pi loses power using NodeJs.
I've found that you can use a signal that the Pi send, SIGPWR, when it loses power.
I made this little test script:
// test.js
var fs = require('fs');
var path = '/home/pi/Documents/Code/surveillanceCam/log/logfile.txt';
fs.writeFileSync(path, new Date().toString() + ': Start\n');
process.on('exit', function () {
fs.appendFileSync(path, new Date().toString() + ': exit\n');
});
process.on('SIGPWR', function () {
fs.appendFileSync(path, new Date().toString() + ': SIGPWR\n');
});
process.stdin.resume();
If I run the script with node test.js I get a line in logfile.txt that end with Start so that works, and if I remove the last line (so the scripts don't run until I stop it), I also get a new line with exit in the end.
But if I keep the last line so the script keeps on running, and then I pull the cable of the Pi, then insert it again. When I go to watch the file after it boots I only get the line with the start in the end..
I want to have 2 lines in my logfile.txt one with the time of start, and one with the time of power loss..
And from what I've read the SIGPWR signal is sent when power is lost. Does the script not have enough time to write to the file or is there something else I can do?
EDIT: What I want to do is to simulate a power loss and when the power is lost write to the file.
EDIT2: I think how I will solve this problem is to add a process.on('SIGINT',...) signal. So when the user ends the program with Ctrl+C I will then and only then write to the file. And then when the node server start I will check if there is something in the file. If there isn't then the node server didn't shut of gracefully and I should display an error.

Answer 1

Unplugging the power would not be a graceful shutdown, and I doubt that you could depend on the reliability of any event for figuring out if it shut down. This is why so many things have troubles recovering when the power goes out, because things are not able to be shut down gracefully. Everything dies before the OS can probably even realize it, so nothing gets gracefully shutdown.

Answer 2

The standard way you detect this sort of situation is by creating flag file when the Pi boots up, and removing it on a normal shutdown.
If the flag file exists next time the Pi starts up (you check before creating it), you know that that Pi crashed for someone reason (you don't know if it was a power loss, kernel panic, or something else).
There is no way to respond directly to a power loss in your code unless you add some sort of battery backup unit that sends the appropriate signal.