Storing state in a Node/Express application

Question

I'm writing a Node/Express app (my first) and need help persisting what feels like a global variable across page loads; but using a global variable feels wrong.

For the purposes of the question, the site is essentially 3 different table views on the same data. The data in the tables is taken from 3 separate MongoDB tables, merged together with a function, and displayed (using Pug, iterating over the object I just created).

The 3 different views are just different Pug templates iterating over the same object.

I have middleware which generates this object from MongoDB and stores it on res.locals, but I don't want to re-generate it by default every time the user selects a different view. The data hasn't changed, and this feels wasteful.

I want to be able to set some sort of variable, dataNeedsToBeUpdated, and if true then the function inside my middleware will actually do the work and regenerate the table; if false, it'll just skip the operation.

If the user performs one of my update operations, I'll set dataNeedsToBeUpdated = true, redirect, middleware will fire, and the data will refresh before the next page load.

How do I do this properly?

Answer 1

app.locals works just about like res.locals, just it's available to the whole app. You can access it in middleware from req.app.locals. The flow as you've described it sounds good; just use app.locals for storing the data and the dataNeedsToBeUpdated.