Expressjs router based on Content-Type header

user_4644434 0
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For routing, I'd like my middleware to pass the request the routes defined in a /html folder to server HTML(ejs), and if header Content-Type is application/json, use the routes defined in the /api folder.

But I don't want to have to define that in every route. So I'm not looking for middleware that defines some req.api property that I can check on in every route 

app.get('/', function(req, res) {
    if(req.api_call) {
        // serve api
    } else {
        // serve html
    }
});

But I'd like something like this:

// HTML folder
app.get('/', function(req, res) {
    res.send('hi');
});

// API folder
app.get('/', function(req, res) {
    res.json({message: 'hi'});
});

Is this possible and if so, how can I do this?

I'd like it to work something like this:

app.use(checkApiCall, apiRouter);
app.use(checkHTMLCall, htmlRouter);
express middleware node.js api
2 Answers

To throw my hat in the ring, I wanted easily readable routes without having .json suffixes everywhere.

router.get("/foo", HTML_ACCEPTED, (req, res) => res.send("<html><h1>baz</h1><p>qux</p></html>"))
router.get("/foo", JSON_ACCEPTED, (req, res) => res.json({foo: "bar"}))

Here's how those middlewares work.

function HTML_ACCEPTED (req, res, next) { return req.accepts("html") ? next() : next("route") }
function JSON_ACCEPTED (req, res, next) { return req.accepts("json") ? next() : next("route") }

Personally I think this is quite readable (and therefore maintainable).

$ curl localhost:5000/foo --header "Accept: text/html"
<html><h1>baz</h1><p>qux</p></html>

$ curl localhost:5000/foo --header "Accept: application/json"
{"foo":"bar"}

Notes:

  • I recommend putting the HTML routes before the JSON routes because some browsers will accept HTML or JSON, so they'll get whichever route is listed first. I'd expect API users to be capable of understanding and setting the Accept header, but I wouldn't expect that of browser users, so browsers get preference.
  • The last paragraph in ExpressJS Guide talks about next('route'). In short, next() skips to the next middleware in the same route while next('route') bails out of this route and tries the next one.
  • Here's the reference on req.accepts.
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