Reduce code repetition in express API route - node.js

Question

I'm learning express and am currently writing an API, and have this structure:
app.route('/api/brief/:_id')
.get(function(req, res, next) {
// Check if the _id is a valid ObjectId
if (mongoose.Types.ObjectId.isValid(req.params._id)) {
// Do something
}else{
// Error
}
})
.put(function(req, res, next) {
// Check if the _id is a valid ObjectId
if (mongoose.Types.ObjectId.isValid(req.params._id)) {
// Do something
}else{
// Error
}
})
.delete(function(req, res, next) {
// Check if the _id is a valid ObjectId
if (mongoose.Types.ObjectId.isValid(req.params._id)) {
// Do something
}else{
// Error
}
});
Ideally I'd like to avoid the repetition (checking the validity of the ID).
Is there a way that I can structure the route as to avoid that repetition?

Answer 1

There are a few ways you can approach it. There is the app.all() method:
app.all("/api/*", function(req, res, next) {
if (req.params._id) {
if (mongoose.Types.ObjectId.isValid(req.params._id)) {
return next();
}
else {
// error handle
}
}
next();
});
Personally, I don't like catch-alls. I'd rather be more explicit:
function validateMongooseId (req, res, next) {
if ( mongoose.Types.ObjectId.isValid(req.params._id) ) {
return next();
}
else {
// error handle
}
}
function handleGet(req, res, next) {}
function handlePost(req, res, next) {}
function handlePut(req, res, next) {}
app.post("/api/brief", handlePost);
app.get("/api/brief/:_id", validateMongooseId, handleGet);
app.put("/api/brief/:_id", validateMongooseId, handlePut);
I put the .post() in there to demonstrate why I don't like the catch-all. It clearly doesn't apply to that endpoint. You may have other middleware functions that apply to it, so I'd rather explicitly have them on the endpoints that use them.