node.js - Exception when attempting to wrap Buffered-writer -

disclaimer: i'm new node (but not javascript).

im trying write logger class, holds few lines @ time in memory, flushes disk when buffer reaching capacity

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problem

calling logger wrapper results in exception in buffered writer

im sure ive misunderstood how require() works, , various people advised me create object using new chatlogs.chatlogger() iti dont see many other node libs using way of working

/www/im/node_modules/buffered-writer/lib/buffered-writer.js:125     cb ();         ^ typeerror: undefined not function     @ writer.flush (/www/nodeim/node_modules/buffered-writer/lib/buffered-writer.js:125:3)     @ chatlogger.close (/www/nodeim/helpers/chatlogs.js:27:14)     @ object.<anonymous> (/www/nodeim/app.js:76:16)     @ module._compile (module.js:456:26)     @ object.module._extensions..js (module.js:474:10)     @ module.load (module.js:356:32)     @ function.module._load (module.js:312:12)     @ function.module.runmain (module.js:497:10)     @ startup (node.js:119:16)     @ node.js:901:3 

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calling code...

var chatlogs = require('./helpers/chatlogs.js');  var chatlogger_obj = new chatlogs.chatlogger();  chatlogger_obj.open("logs/log.txt"); chatlogger_obj.log("testing"); chatlogger_obj.close();  process.exit(0); 

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wrapper class

./helpers/chatlogs.js

exports.version = '0.0.1';  var    buffer = require('buffered-writer'),     fs = require('fs');  var chatlogger = function() {     this.handle = null,     this.filename = "",     this.dirtyops = 0; }  chatlogger.prototype.open = function (filename) {      //fs.unlink(filename);      this.filename = filename;     this.handle = buffer.open(filename)         .on ("error", function (error) {             //this.handle = null;             console.log (error);         }); }  chatlogger.prototype.close = function() {     console.log("closing");     this.handle.flush();     this.handle.close();     this.handle = null; }  chatlogger.prototype.log = function (str) {      console.log(str);     this.handle.writeln(str);      if (this.dirtyops++ > 5)     {         console.log("flushing");         this.handle.flush();         this.dirtyops = 0;     } }  module.exports.chatlogger = chatlogger; 

i'm author of module. need pass callback flush function, don't need call flush. when buffered-writer closes or exceed buffer size when writing, data automatically flushed disk.

writer#flush(callback)