express.js compress middleware do not work

Question

I have the following middlewares in my app:

app.use(express.favicon(__dirname + '/static/public/images/favicon.ico'));
app.use(express.compress());
app.use(express.json());
app.use(express.urlencoded());
app.use(express.cookieParser('SECRET!'));
app.use(express.static(__dirname + config.static_path, {maxAge: 365 * 86400000}));
app.use(express.session({secret: 'SECRET!'}));
app.use(flash());
app.use(passport.initialize());
app.use(passport.session());
app.use(app.router);

headers example:

But the static content do not compressing. What could be the problem?

Answer 1

There are several reasons why your static content may not get compressed:

• express.compress maintains a minimum file size threshold; files with a size below this threshold (default: 1024 bytes) won't get compressed;
• express.compress also maintains a whitelist of content types to compress; if you're serving files with a content type that's not on that list, it won't get compressed either;

To fix:

app.use(express.compress({
  threshold : 0, // or whatever you want the lower threshold to be
  filter    : function(req, res) {
    var ct = res.get('content-type');
    // return `true` for content types that you want to compress,
    // `false` otherwise
    ...
  }
}));

(as a reference, this is the default filter function used)