node.js - which functions done/next are bound to in mongoos pre/save/(serial/parallel) middleware -

trying understand mongoose middleware (pre/save/parallel) thru docs/blogs(tim casewell).

based on http://mongoosejs.com/docs/middleware.html

var schema = new schema(..); schema.pre('save', true, function (next, done) {   // calling next kicks off next middleware in parallel   next();   doasync(done); });  hooked method, in case save, not executed until done called each middleware. 

what done/next bound here? can please give complete example of how use it?

for eg: use serial follows:

mymodel.save(function(err) {   if (err)      console.error("error occured")   else     console.info("document stored"); });  schema.pre('save', function(next) {   if (!self.validatesomething()) {     next(new error());   } else {     next();   } }); 

what next bound here? needs bound executed? fail understand function(s) next/done referring to?

if elaborate control flow code above, great help.

-------------this elaborate understanding (not part of question)------

   * on executing mymodel.save(...)    * control flow passed pre/save    * if self.validatesomething() fails,      * document not tried saved in db      * "error occurred" printed on console    * if validation succeeds,      * control flow should passed *somewhere* in mongoose libs         * document tried save in db          * on success, "document saved" printed on console          * on failure, "error occurred" printed on console 

they're bound functions provide flow control internally within mongoose. mongoose depends on hooks-js middleware functionality, see source more details.

for example, if have multiple pre-save middleware functions, next call function call next pre-save middleware or on error, pass error save callback.

using done more advanced option flow control, allowing multiple pre-save, example, middleware execute @ once, not moving past pre-save step until done has been called in middleware functions.