Difference between app use and app get in express js

Question

I m kind of new to express and node js  and I can t figure out the difference between app use and app get  It seems like you can use both of them to send information  For example   app use     function req  res next        res send  Hello        next          seems to be the same as this   app get      function  req res       res send  Hello

User · Answer

app use is the  lower level  method from Connect  the middleware framework that Express depends on   Here s my guideline    Use app get if you want to expose a GET method  Use app use if you want to add some middleware  a handler for the HTTP request before it arrives to the routes you ve set up in Express   or if you d like to make your routes modular  for example  expose a set of routes from an npm module that other web applications could use

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Difference between app use  amp  app get   app use   It is generally used for introducing middlewares in your application and can handle all type of HTTP requests   app get   It is only for handling GET HTTP requests   Now  there is a confusion between app use  amp  app all  No doubt  there is one thing common in them  that both can handle all kind of HTTP requests  But there are some differences which recommend us to use app use for middlewares and app all for route handling    app use     It takes only one callback   app all     It can take multiple callbacks  app use   will only see whether url starts with specified path  But  app all   will match the complete path    For example     app use    book    middleware      will match  book    will match  book author    will match  book subject  app all    book    handler      will match  book    won t match  book author       won t match  book subject      app all    book      handler      won t match  book            will match  book author    will match  book subject    next   call inside the app use   will call either the next middleware or any route handler  but next   call inside app all   will invoke the next route handler  app all    app get post put    etc   only  If there is any middleware after  it will be skipped  So  it is advisable to put all the middlewares always above the route handlers

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app use   is intended for binding middleware to your application  The path is a  mount  or  prefix  path and limits the middleware to only apply to any paths requested that begin with it  It can even be used to embed another application      subapp js var express   require  express    var app   modules exports   express                server js var express   require  express    var app   express     app use   subapp   require    subapp               By specifying   as a  mount  path  app use   will respond to any path that starts with    which are all of them and regardless of HTTP verb used    GET   PUT  foo POST  foo bar etc    app get    on the other hand  is part of Express  application routing and is intended for matching and handling a specific route when requested with the GET HTTP verb    GET     And  the equivalent routing for your example of app use   would actually be   app all          function  req  res        res send  Hello             Update  Attempting to better demonstrate the differences    The routing methods  including app get    are convenience methods that help you align responses to requests more precisely  They also add in support for features like parameters and next  route     Within each app get   is a call to app use    so you can certainly do all of this with app use   directly  But  doing so will often require  probably unnecessarily  reimplementing various amounts of boilerplate code   Examples    For simple  static routes   app get      function  req  res                   vs   app use      function  req  res  next      if  req method      GET     req url              return next                   With multiple handlers for the same route   app get      authorize  ADMIN    function  req  res                   vs   const authorizeAdmin   authorize  ADMIN     app use      function  req  res  next      if  req method      GET     req url              return next       authorizeAdmin req  res  function  err        if  err  return next err                          With parameters   app get   item  id   function  req  res      let id   req params id                 vs   const pathToRegExp   require  path-to-regexp     function prepareParams matches  pathKeys  previousParams      var params   previousParams              TODO  support repeating keys      matches slice 1  forEach function  segment  index        let   name     pathKeys index       params name    segment           return params     const itemIdKeys       const itemIdPattern   pathToRegExp   item  id   itemIdKeys    app use      function  req  res  next      if  req method      GET   return next       var urlMatch   itemIdPattern exec req url     if   urlMatch  return next       if  itemIdKeys  amp  amp  itemIdKeys length      req params   prepareParams urlMatch  itemIdKeys  req params      let id   req params id                     Note  Express  implementation of these features are contained in its Router  Layer  and Route

User · Answer

There are 3 main differences I have found till now  The 3rd one is not so obvious and you may find it interesting  The differences are the same for the express router  That means router use   and router get   or other post  put  all  etc methods has also same difference   1   app use path  callback  will respond to any HTTP request  app get path  callback  will only respond to GET HTTP request  In the same way  post  put  etc will respond to their corresponding request  app all   responds to any HTTP request so app use   and app all   are the same in this part   2  app use path  callback  will match the prefix of the request path and responds if any prefix of the request path matches the path parameter  Such as if the path parameter is  quot   quot   then it will match  quot   quot    quot  about quot    quot  users 123 quot  etc  app get path  callback  Here get will match the whole path  Same for other HTTP requests and app all    Such as  if the path parameter is  quot   quot   then it will only match  quot   quot    3 next  route   doesn t work on the middleware callback functions of app use    It works only on app get    app all   and other similar function of other HTTP requests  According to express documentation   next  route   will work only in middleware functions that were loaded by using the app METHOD   or router METHOD   functions  METHOD is the HTTP method of the request that the middleware function handles  such as   GET  PUT  or POST  in lowercase   From here we will use the keyword METHOD instead of get  post  all  etc  But what is next  route     Let s see  next  route   we see  app use   or app METHOD   can take several callback middleware functions  From the express documentation   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  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   So we see each middleware functions have to either call the next middleware function or end the response  And this is same for app use   and app METHOD    But sometimes in some conditions  you may want to skip all the next callback functions for the current route but also don t want to end the response right now  Because maybe there are other routes which should be matched  So to skip all the callback functions of the current route without ending the response  you can run next  route    It will skip all the callback functions of the current route and search to match the next routes  For Example  From express documentation   app get   user  id   function  req  res  next         if the user ID is 0  skip to the next route   if  req params id      0   next  route        otherwise pass the control to the next middleware function in this stack   else next      function  req  res  next         send a regular response   res send  regular          handler for the  user  id path  which sends a special response app get   user  id   function  req  res  next      res send  special       See  here in a certain condition req params id      0   we want to skip the next callback function but also don t want to end the response because there is another route of the same path parameter which will be matched and that route will send a special response   Yeah  it is valid to use the same path parameter for the same METHOD several times  In such cases  all the routes will be matched until the response ends   So in such cases  we run the next  route   and all the callback function of the current route is skipped  Here if the condition is not met then we call the next callback function  This next  route   behavior is only possible in the app METHOD   functions  Recalling from express documentation   next  route   will work only in middleware functions that were loaded by using the app METHOD   or router METHOD   functions   Since skipping all callback functions of the current route is not possible in app use    we should be careful here  We should only use the middleware functions in app use   which need not be skipped in any condition  Because we either have to end the response or traverse all the callback functions from beginning to end  we can not skip them at all  You may visit here for more information

User · Answer

app get is called when the HTTP method is set to GET  whereas app use is called regardless of the HTTP method  and therefore defines a layer which is on top of all the other RESTful types which the express packages gives you access to

User · Answer

In addition to the above explanations  what I experience   app use   book   handler       will match all requests beginning with   book  as URL  so it also matches   book 1  or   book 2   app get   book       matches only GET request with exact match  It will not handle URLs like   book 1  or   book 2   So  if you want a global handler that handles all of your routes  then app use      is the option  app get      will handle only the root URL

User · Answer

Simply  app use means    Run this on ALL requests     app get means    Run this on a GET request  for the given URL

[node.js] Difference between app.use and app.get in express.js

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