CODEWITHSUNDEEP
javascriptnode.jsmodule
Kathandrax
Kathandrax

Reputation: 1054

Modules and Node.js

I'm trying to learn Node.js basics by doing the learnyounode lessons. I am stuck at the Make it Modular chapter.

I don't know if I'm allowed to paste its content here, but roughly, I am asked to create a module to filter file names in a directory following a specified extension.

Here is what I've done so far:

var module = require('module');

module(process.argv[2], process.argv[3], function (err, data){
  if(err){
    console.log("Error");
  }
  else{
    console.log(data);
  }
});

module.js:

var fs = require('fs');
var path = require('path');

module.exports = function (dir, ext, callback){
  fs.readdir(dir, function (err, files){
    if(err){
      callback(err);
    }
    else {
      var array = '';
      for(var i=0; i<files.length; i++){
        if(path.extname(files[i]) === '.'+ext){
         array+=files[i]+"\n";
        }
      }
      callback(null, array);
    }
  });
}

I get the following error:

module.js:27
  this.id = id;
          ^

TypeError: Cannot set property 'id' of undefined
    at Module (module.js:27:11)
    at Object.<anonymous> (/home/maxence/Documents/Node.js/learnyounode/MIM/mim.js:3:1)
    at Module._compile (module.js:397:26)
    at Object.Module._extensions..js (module.js:404:10)
    at Module.load (module.js:343:32)
    at Function.Module._load (module.js:300:12)
    at Module.require (module.js:353:17)
    at require (internal/module.js:12:17)
    at Object.<anonymous> (/usr/local/lib/node_modules/learnyounode/node_modules/workshopper-wrappedexec/exec-wrap.js:87:3)
    at Module._compile (module.js:397:26)

My guess is I've not declared a variable correctly somewhere in my code but I can't manage to find it. Is the call of the module correct?

Best regards, MM

EDIT : as gnerkus said, there should be './module' instead of 'module'. Here is the working code:

var module = require('./module');

module(process.argv[2], process.argv[3], function (err, data){
  if(err){
    console.log("Error");
  }
  else{
    console.log(data);
  }
});

module.js:

var fs = require('fs');
var path = require('path');

module.exports = function (dir, ext, callback){
  fs.readdir(dir, function (err, files){
    if(err){
      callback(err);
    }
    else {
      var array = '';
      for(var i=0; i<files.length; i++){
        if(path.extname(files[i]) === '.'+ext){
         array+=files[i]+"\n";
        }
      }
      callback(null, array);
    }
  });
}

EDIT 2: it seems that this version is to be preferred:

var module = require('./module');

module(process.argv[2], process.argv[3], function (err, data){
  if(err){
    console.log("Error");
  }
  else{
    for(var i=0; i<data.length; i++){ 
      console.log(data[i]);
    }
  }
});

module.js:

var fs = require('fs');
var path = require('path');

module.exports = function (dir, ext, callback){
  fs.readdir(dir, function (err, files){
    if(err){
      callback(err);
    }
    else {
      var array = [];
      for(var i=0; i<files.length; i++){
        if(path.extname(files[i]) === ('.'+ext)){
         array.push(files[i]);
        }
      }
      callback(null, array);
    }
  });
}

Both are correct, but the second version is required to complete the chapter.

Upvotes: 0

Views: 175

Answers (1)

gnerkus
gnerkus

Reputation: 12019

The error occurs because you're requiring a node module and not your custom module. From the NodeJS documentation:

If the module identifier passed to require() is not a native module, and does not begin with '/', '../', or './', then Node.js starts at the parent directory of the current module, and adds /node_modules, and attempts to load the module from that location. Node will not append node_modules to a path already ending in node_modules.

solution.js

var myModule = require('./module');
// The rest of your code.

Upvotes: 1

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