Does express.static() cache files in the memory?

问题:

In ExpressJS for NodeJS, we can do the following:

app.use(express.static(__dirname + '/public'));

to serve all the static CSS, JS, and image files. My questions are these:

1) When we do that, does Express automatically cache the files in the server's memory or does it read from the hard disk every time one of the resources is served?

2) When we do that, does Express, using ETag by default, save the resources on the client's hard disk, or on the client's memory only?

回答1:

1. The static middleware does no server-side caching. It lets you do two methods of client-side caching: ETag and Max-Age:

If the browser sees the ETag with the page, it will cache it. The next time the browser loads the page it checks for the ETag number changes. If the file is exactly the same, and so is its ETag - the server responds with an HTTP 304("not modified") status code instead of sending all the bytes again and saves a bunch of bandwidth. Etag is turned-on by default but you can turn it off like this:

app.use(express.static(myStaticPath, {
  etag: false
}))

Max-age is will set the max-age to some amount of time so the browser will only request that resource after one day has passed.

app.use(express.static(myStaticPath, {
  maxAge: '5000' // uses milliseconds per docs
}))

For more details you can read this article

2. By default it's on the hard-drive, but someone can use something like this