javascript - Why the added prototype method should be added after `util.inherits`? -


i want know why added prototype method should added after util.inherits?

var util = require('util'); var eventemitter = require('events').eventemitter;  function server() {     console.log('init'); }  server.prototype.say = function(){     console.log('say'); }  util.inherits(server, eventemitter);  var server = new server(); server.on('abc', function(){     console.log('abc'); })  server.emit('abc'); server.say();

there error when run code:

c:\users\elqstux\desktop\wy.js:19 server.say();        ^ typeerror: undefined not function     @ object.<anonymous> (c:\users\elqstux\desktop\wy.js:19:8)     @ module._compile (module.js:460:26)     @ object.module._extensions..js (module.js:478:10)     @ module.load (module.js:355:32)     @ function.module._load (module.js:310:12)     @ function.module.runmain (module.js:501:10)     @ startup (node.js:129:16)     @ node.js:814:3

but if modified code this:

util.inherits(server, eventemitter);  server.prototype.say = function(){     console.log('say'); }

the code runs ok.

from node.js documentation https://nodejs.org/docs/latest/api/util.html#util_util_inherits_constructor_superconstructor:

util.inherits(constructor, superconstructor)

inherit prototype methods 1 constructor another. the prototype of constructor set new object created superconstructor.

so after use util.inherits on server, prototype replaced new, inheriting eventemitter, hence added methods lost.


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