Question 191442 in Javascript Question posted in
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Javascript – is <Function> similar as (req,res)

i am new to nodejs. referring to this link section http.createServer([options][, requestListener])
i know how to create the options object. but for the [, requestListener], it is stated in the docs that it is a <Function>. when i clicked on the link of <Function> which is here
it indicates that that <Function> is a normal function that could be lambda, however, in the docs of http.createServer([options][, requestListener]) as stated in the first link, it demonstrate the following:

http.createServer((req, res)

as far as i understood, the (req, res) is two different callbacks not a normal <Function>
to some extent. i am slightly befuddled.

1.would you please show me the difference between (req,res) and <Function>

2.where in docs (req,res) are explained. i want to know how can i configure or access properties of either of req and res

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2

Answers


  1. 0

    You are misreading the code. (req, res) is not a parameter to createServer. This entire thing is an arrow function expression, a way to define an anonymous function:

    (req, res) => {
  res.writeHead(200, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify({
    data: 'Hello World!',
  }));
}

    It is largely (but not completely) equivalent to:

    function serverHandler(req, res) {
  res.writeHead(200, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify({
    data: 'Hello World!',
  }));
}

    The differences (not really important here, but for completeness’ sake) are: the latter can be a function expression or a function statement, while the former is always an expression; the former does not redefine this while the latter does; and the former is not assigned to a variable, while the latter may be (serverHandler in this case).

    Given the latter definition of serverHandler, you could use it as follows:

    http.createServer(serverHandler)

    An anonymous arrow function expression is just doing the same job as a function identifier in this latter example.

    EDIT on where to find more documentation on req and res:

    Per documentation of createServer:

    The requestListener is a function which is automatically added to the 'request' event.

    Per documentation of 'request' event, the event callback gets two parameters: request, an instance of IncomingMessage, and response, an instance of ServerResponse.

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  2. 0

    The req and res arguments to the callback are the same as the request and response properties of the corresponding request event.

    Event: ‘request’
    Added in: v0.1.0

    You can then follow the links to the documentation of those datatypes to see how you use them in your server.

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