If I change position of req with res for example (res,req)=>{ res.send();}
the server shows error that res.send is not a function.
My question is are we restricted with positioning the req,res objects?
why it throws the error the res.send() is not a function or why is it trying to see it as a function?
(res,req) => {res.send();}
is a function with two parameters. When it is invoked by the express framework, the first will be passed a request object (which has no .send function) and the second will be passed a response object (which has a .send function). Your code wants to invoke the .send function of the first object (which you misleadingly call res), but that first object is a request and has no .send function.
See the express API documentation here.
You can change the variable name, can push new variables to request but you can not change functionality of internal request and response object. And as per request functionality , it accepts what you send in request and Send() is not part of request.
Related
is it possible to extract and set as variable the "Payload Request" which has been pushed in order to receive particular response?
You can access the request object in the callback function by response.request.
This object is the request object itself, so it contains everything you passed in the request. It doesn't have a "payload" attribute though.
The equivalent should be response.request.body, assuming you had a body in the request. Everything else is still there, headers, cookies, meta, method, etc
More on the params of request here.
If request object is not being used inside api callback function should i remove it from parameters of callback. I think it does not make a difference but i am curious what is the practice.
app.get('/', function (req, res) {
res.send('hello world')
})
The req in params of callback function
It does make a difference.
If you were to remove that first parameter, then this code would not longer work, you would get an error like
res.send is not a function.
That's because the express .get method is going to insert the request object as the first parameter, and the response object as the second paremeter.
If you were to remove 'req' as the first parameter, the request object would still be passed as the first parameter. There's no stopping express from doing that.
As a convention, if for example ESLint is giving you issues re: unused-vars, you can prefix unused first parameters with an underscore, like _res.
Now if you're talking about subsuqent parameters on the otherhand, it's fine to leave them off, which is in fact what you're doing here, you can see from the express documentation that the callback also accepts a third argument, next, which you're not declaring or using here.
I have a nodejs function in Lambda that works fine. However when I try to integrate it with Zapier. The function doesn’t return a value to Zapier. Is their a specific way to callback your function in lambda so that Zapier can receive the returned values?
Well, you can show as some code to get an idea. My guess is that you return an object to Zapier, while Zapier always expects an array of data. If I am correct, try to wrap your object in array before send.
I see it is used in various ways: next(), next('route'), next(error)...
Where can I find the official documentation for the next() method?
I don't find any documentation summing up it's use cases on the express api docs...
UPDATE:
From what I coroborated, next works like this:
next() : sends req to the next middleware function of the current route
next('route'): sends req to next matching route
and less obvious...
next(anythingElse) sends req to the next error handling middleware, where err will be equal to anythingElse
You can view the "callback" argument under app.use() at http://expressjs.com/en/4x/api.html#app.use
There are also middleware callback function examples as well (http://expressjs.com/en/4x/api.html#middleware-callback-function-examples)
You are looking at the wrong page in the express documentation. The next callback is just to initiate/continue the request-response cycle. The actual guide is located under "Using middleware" title of Guides section on the Expressjs website.
Middleware functions are functions that have access to the request
object (req), the response object (res), and the next middleware
function in the application’s request-response cycle. The next
middleware function is commonly denoted by a variable named next.
Middleware functions can perform the following tasks:
Execute any code.
Make changes to the request and the response objects.
End the request-response cycle.
Call the next middleware function in the stack.
If the current middleware function does not end the request-response
cycle, it must call next() to pass control to the next middleware
function. Otherwise, the request will be left hanging.
A simple question, if I have a route setup with a chain of callbacks e.g.
app.route('/myroute').post(callback1, callback2, callback3);
I call next() on each of my callback, except the last one.
Suppose I use my 'res' object to render and send back a response on callback2 but I still want to do some processing on callback3 which does not need to interact with the client or return anything.
Will my callback3 be always executed even if callback1 or callback2 uses the res object to return a response?
Doing some tests shows that it does call callback3 but some say expressjs will terminate the call chain if res returns a response. So I don't want to have any doubts, is there a clear answer on the behaviour here?
If you are calling next() in callback2, then the code in callback3 will be executed. The only thing that has "finished" in callback2 is the HTTP request. The connection will be closed, as you've sent a response already. Any further attempts to send a response afterwards will result in: Error: Can't render headers after they are sent to the client.