How can I set response header on express.js assets

This is so annoying.

Okay if anyone is still having issues or just doesn't want to add another library. All you have to do is place this middle ware line of code before your routes.

Cors Example

app.use((req, res, next) => {
    res.append('Access-Control-Allow-Origin', ['*']);
    res.append('Access-Control-Allow-Methods', 'GET,PUT,POST,DELETE');
    res.append('Access-Control-Allow-Headers', 'Content-Type');
    next();
});

// Express routes
app.get('/api/examples', (req, res)=> {...});

There is at least one middleware on npm for handling CORS in Express: cors. [see @mscdex answer]

This is how to set custom response headers, from the ExpressJS DOC

res.set(field, [value])

Set header field to value

res.set('Content-Type', 'text/plain');

or pass an object to set multiple fields at once.

res.set({
  'Content-Type': 'text/plain',
  'Content-Length': '123',
  'ETag': '12345'
})

Aliased as

res.header(field, [value])