[Node.js] 4. Modules

4.2 Missing Exports

Notice the two different files: high_five.js on the left side andapp.js on the right. The code as it's written will not work,high_five.js isn't exporting anything.

Add the proper exports line to have a successful high five!

//high_five.js

var highfive = function() {
  console.log("smack!!");
};
module.exports = highfive;

//app.js

var highfive = require('./high_five.js');
highfive();

Export A Function

Notice the app.js file with the myRequest function below. Let's refactor myRequest out to its own my_request.js module.

Move the myRequest function and the http require into my_request.js

var http = require('http');

var myRequest = function(message) {
  var request = http.request('http://codeschool.com', function(response) {
    response.pipe(process.stdout, { end: false });
  });

  request.write(message);
  request.end();
};

myRequest('Hello, this is dog.');

Answer:

// app.js

myRequest('Hello, this is dog.');

//my_request.js

var http = require('http');

var myRequest = function(message) {
  var request = http.request('http://codeschool.com', function(response) {
    response.pipe(process.stdout, { end: false });
  });

  request.write(message);
  request.end();
};

myRequest('Hello, this is dog.');

Export the myRequest function.

module.exports = myRequest;

Require the my_request.js module in app.js.

var myRequest = require('./my_request');
myRequest('Hello, this is dog.');

Exporting An Object

The app.js code on the right side does not work. Once again we forgot to export our functions.

In the logger.js file, export the info function so we can use it in app.jsby assigning it to the exports object.

app.js

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

logger.info('This is some information');
logger.warn('something bad is happening');

logger.js

var warn = function(message) {
  console.log("Warning: " + message);
};

var info = function(message) {
  console.log("Info: " + message);
};

var error = function(message) {
  console.log("Error: " + message);
};

Answer:

exports.info = function(message) {
  console.log("Info: " + message);
};

In the logger.js file, export the warn function so we can use it in app.jsby assigning it to the exports object.

exports.warn = function(message) {
  console.log("Warning: " + message);
};

In the logger.js file, export the error function so we can use it in app.jsby assigning it to the exports object.

exports.error = function(message) {
  console.log("Error: " + message);
};

4.5 Installing Local Modules

Practice using npm by installing the npm module underscore using the npm installcommand.

npm install underscore

4.6 Installing Global Modules

Now install the coffee-script module, but install it globally so you can use the coffeeexecutable that comes with coffee-script.

npm install coffee-script -g

4.7 Dependency

Add two dependencies to our package.json file, connect andunderscore. We'll want to use version 2.1.1 of connect and version1.3.3 of underscore.

Add the connect dependency to package.json

Add the underscore dependency to package.json

{
  "name": "My Awesome Node App",
  "version": "1",
  "dependencies": {
    "connect": "2.1.1",
      "underscore": "1.3.3"
  }
}

4.8 Semantic Versioning

We want to make sure we are always up-to-date with the most recent patch-level changes to our dependencies when we run npm install.

Update the connect version on package.json to fetch the latest patch-levelchanges. All we have to do is add one character to the beginning of the version number.

{
  "name": "My Awesome Node App",
  "version": "1",
  "dependencies": {
    "connect": "~2.2.1",
    "underscore": "1.3.3"
  }
}

Now update the underscore version on package.json to fetch the latestpatch-level changes. Again, all we have to do is add one character to the beginning of the version number.

{
  "name": "My Awesome Node App",
  "version": "1",
  "dependencies": {
    "connect": "~2.2.1",
    "underscore": "~1.3.3"
  }
}