What are res and req parameters in Express functions

Question

In the following Express function   app get   user  id   function req  res       res send  user    req params id         What are req and res  What do they stand for  what do they mean  and what do they do   Thanks

User · Answer

Request and response   To understand the req  try out console log req

User · Answer

req is an object containing information about the HTTP request that raised the event   In response to req  you use res to send back the desired HTTP response   Those parameters can be named anything   You could change that code to this if it s more clear   app get   user  id   function request  response     response send  user     request params id         Edit   Say you have this method   app get   people json   function request  response          The request will be an object with properties like these  just to name a few     request url  which will be   people json  when this particular action is triggered request method  which will be  GET  in this case  hence the app get   call  An array of HTTP headers in request headers  containing items like request headers accept  which you can use to determine what kind of browser made the request  what sort of responses it can handle  whether or not it s able to understand HTTP compression  etc  An array of query string parameters if there were any  in request query  e g   people json foo bar would result in request query foo containing the string  bar      To respond to that request  you use the response object to build your response   To expand on the people json example   app get   people json   function request  response         We want to set the content-type header so that the browser understands       the content of the response    response contentType  application json          Normally  the data is fetched from a database  but we can cheat    var people           name   Dave   location   Atlanta           name   Santa Claus   location   North Pole           name   Man in the Moon   location   The Moon               Since the request is for a JSON representation of the people  we       should JSON serialize them  The built-in JSON stringify   function       does that    var peopleJSON   JSON stringify people         Now  we can use the response object s send method to push that string       of people JSON back to the browser in response to this request    response send peopleJSON

User · Answer

I noticed one error in Dave Ward s answer  perhaps a recent change    The query string paramaters are in request query  not request params   See https   stackoverflow com a 6913287 166530     request params by default is filled with the value of any  component matches  in routes  i e   app get   user  id   function request  response     response send  user     request params id         and  if you have configured express to use its bodyparser  app use express bodyParser      also with POST ed formdata   See How to retrieve POST query parameters

[node.js] What are "res" and "req" parameters in Express functions?

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