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Last active April 2, 2022 12:49
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Persistent state in Node.js

This is an extremely simple example of how you have 'persistent state' when writing an application in Node.js. The i variable is shared across all requests, so every time the /increment route is accessed, the number is incremented and returned.

This may seem obvious, but it works quite differently from eg. PHP, where each HTTP request is effectively a 'clean slate', and you don't have persistent state. Were this written in PHP, then every request would have returned 1, rather than an incrementing number.

var i = 0;
// [...]
app.get("/increment", function(req, res) {
i += 1;
res.send("Current number: " + i);
// [...]
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