Node.js /变量和模块的继承

Question

I have trouble with inheritance in node.js. I have the following code:

Main.js relavnt code:

var s3_prototype_require = require("./s3")
var s3_prototype = new s3_prototype_require();

function getDoc(file) {
        s3_prototype.read(file, function(err) {
            return_result(res, err);
        })
     }

server,js relvant code:

var server = function(){};
var idx = 0;    
var winston = require('winston')
var logger = new(winston.Logger)({
    transports: [
        new(winston.transports.File)({
            stream: fs.createWriteStream(log_g, {
                flags: 'a'
            }),
            options: {
                highWaterMark: 32
            }
        })
    ]
});

module.exports = server;

s3.js relvant code:

var server= require('./server'),
util = require('util');

var s3 = function() {
  this.s3 = 's3';
};

util.inherits(server, s3);

s3.prototype.read = function(file, callBack) {
     logger.info("Read file...");
     idx = idx + 1;     
}

The problem is that I failed on the following error: ReferenceError: logger is not defined . This is despide the fact I defined the logger variable in the server.js code. Similar problem happens with the idx variable.

How I define variable and modules Inheritance in node.js (like protected in Java)?

Answer 1

How I define variable and modules Inheritance in node.js (like protected in Java)?

Objects in JavaScript are a little different from your traditional objects in languages like Java. Objects can't really have protected values, but you can have inheritance by utilizing prototypes through prototypical inheritance . With your particular problem, you just need to define your server variable with its respective properties so that they can be initialized when you create instances of your object.

The problem lies with your server.js . You define logger , along with some other variables, locally within that file, but you only export the server variable, which is unrelated to these other variables.

// You're only exporting this function
var server = function(){};

// These are not being exported and just live within this file.
var idx = 0;    
var winston = require('winston')
var logger = new(winston.Logger)({
    transports: [
        new(winston.transports.File)({
            stream: fs.createWriteStream(log_g, {
                flags: 'a'
            }),
            options: {
                highWaterMark: 32
            }
        })
    ]
});

module.exports = server;

To fix this, try assigning your server object these variables as properties.

Maybe something like this (I cant't test it so there may be some tweaking that needs to be done)

var server = function(){
    this.idx = 0;
    this.winston = require('winston');
    this.logger = new(winston.Logger)({
        transports: [
            new(winston.transports.File)({
                stream: fs.createWriteStream(log_g, {
                    flags: 'a'
                }),
                options: {
                    highWaterMark: 32
                }
            })
        ]
    });
};

module.exports = server;

Answer 2

Simple solution would be to export an object.

server.js

module.exports = {
  server: server,
  logger: logger
};

s3.js

var serverObj = require('./server');
var server = serverObj.server;
var logger = serverObj.logger;

However I suggest moving the logger related code to it's own file for the sake of separation of concerns .

var server = require('./server');
var logger = require('./logger');