When using the Express router, the usual sequence of events is to detect the route, examine the request, perform some action, then send back the response. It’s quite likely that the action to be performed is asynchronous, so that’s better done with promises than a potentially confusing series of callbacks. I was working on a generic way of handling promises as middleware, and came across this post. I’ve tweaked that a little and here’s the final result.
Handling a route
I’m using a standard way of handling a route, and don’t need to care if it’s asynchronous or not.
Here’s an example route whose action is asynchronous, and returns a promise to its completion
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app.get("/:bosskey/:mode", function(req, res) { res.prom(Process.reqGetKey(req)); }); |
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// appengine health check app.get('/_ah/health', function(req, res) { res.prom(Process.ping()); }); |
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app.get('/info', function(req, res) { res.prom(Promise.resolve({ ok: true, code: 200, info: { api:'effex-api', version:'1.0' }})); }); |
The middleware
In Express.js you can use middleware to incrementally process a request, so the res.prom method has been implemented as middleware as follows, which takes care of stringifying and sending the result when completed.
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// this is a middleware to handle promises in the router function prommy(req, res, next) { res.prom = function(prom) { prom.then(function(result) { res.json(result); }) .catch(function(error) { res.json(error); }); }; next(); } |
Using the middleware
Injecting this into the chain of middleware, is just this
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