The website gives me a notification saying "looks like you're based in the Netherlands..." regarding VAT. Interesting approach, but alas I'm in Belgium (next to NL) and not even close to the border.. :)
The endpoint returning the string of "Looks like you're based in Netherlands" is a nodej.js script that has this defined in the top:
const MESSAGE = "Hey - it looks like you're based in $countryName."
module.exports.getDiscountData = function(countryCode, countyName, etc) {
// Fetch the right message
let message = counryValues[countryCode]; // We get MESSAGE
message = MESSAGE.replace("$countryName", countryName) // oops - we overwrote MESSAGE with a new value!
message = MESSAGE.replace("$otherVariable", etc)
return message; And for each country, I have keys /values listed, like: "GB": MESSAGE, "NL": MESSAGE, "HU": MESSAGE_2
The problem was that once the first request replaced the country name, MESSAGE was mutated, and it now had the value "Hey - it looks like you're based in Netherlands." instead of "Hey - it looks like you're based in $countryName."
I had no idea this would happen. And that a "const" in Javascript is a mutable thing. I fixed it by deep copying the string of the original message.
The super interesting part is that I did not notice this problem, as when I was testing, I did low frequency testing. As I am using Lambda, I probably got a new container created, where MESSAGE was re-initialized. But with the HN traffic, the containers stayed alive longer, making this mutated string issue a problem.
By JS strings are immutable, and String.prototype.replace doesn't modify in place, it returns a fresh string. So, this shouldn't be possible as described.
Thanks for writing the book!
Your website appears to be recognizing me as from the US, which is correct. For whatever value that anecdote is worth to you.
I do live near a border and YouTube thinks I'm in the other country all the time. I suspect European borders may have more resolution than Californian algorithms.