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--- wiki2:nodejs:patterns [2017/05/11 11:09]
alfred [Modules]
+++ wiki2:nodejs:patterns [2020/05/09 09:25] (actual)
@@ Línea 88: / Línea 88: @@
 });
 </code>
+Dependency injection is a software design pattern in which one or more dependencies (or services) are injected, or passed by reference, into a dependent object.
+Dependency injection is really helpful when it comes to testing. You can easily mock your modules' dependencies using this pattern.
+<code>
+var db = require('db');
+// do some init here, or connect
+db.init();
+var userModel = require('User')({
+  db: db
+});
+userModel.create(function (err, user) {
+});
+</code>
+<code>
+var test = require('tape');
+var userModel = require('User');
+test('it creates a user with id', function (t) {
+  var user = {
+    id: 1
+  };
+  var fakeDb = {
+    query: function (done) {
+      done(null, user);
+    }
+  }
+  userModel({
+    db: fakeDb
+  }).create(function (err, user) {
+    t.equal(user.id, 1, 'User id should match');
+    t.end();
+  })
+});
+</code>
+<code>
+function userModel (options) {
+  var db;
+  if (!options.db) {
+    throw new Error('Options.db is required');
+  }
+  db = options.db;
+  return {
+    create: function (done) {
+      db.query('INSERT ...', done);
+    }
+  }
+}
+module.exports = userModel;
+</code>
+In the example above we have two different dbs. In the index.js file we have the "real" db module, while in the second we simply create a fake one. This way we made it really easy to inject fake dependencies into the modules we want to test.
 ===== Middleware / Pipeline =====
@@ Línea 135: / Línea 196: @@
 </code>
-code>
+<code>
     // app.js
     require('./foo.js');
@@ Línea 248: / Línea 309: @@
     qux.log();
 </code>
+===== Callback convention =====
+Modules should expose an error-first callback interface.
+The next example checks, if an Error happened during the execution. You should always check for them.
+<code>
+function readJSON(filePath, callback) {
+  fs.readFile(filePath, function(err, data) {
+    var parsedJson;
+    // Handle error
+    if (err) {
+       return callback(err);
+    }
+    // Parse JSON
+    try {
+      parsedJson = JSON.parse(data);
+    } catch (exception) {
+      return callback(exception);
+    }
+    // Everything is ok
+    return callback(null, parsedJson);
+  });
+}
+</code>
+===== Some good practices =====
+Try to avoid ''this'' and ''new''. Node involves passing around lots of callbacks, and heavy use of higher-level functions to manage control flow. Using a functional style will save you a lot of trouble. Of course, there are some cases, when prototypes can be more efficient, but if possible, try to avoid them.
+Start a new project with npm init. The init command helps you create the application's package.json file. It sets some defaults, which can be later modified. Start writing your fancy new application should begin with:
+<code>
+mkdir my-awesome-new-project
+cd my-awesome-new-project
+npm init
+</code>
+Specify a start and test script. In your package.json file you can set scripts under the scripts section. By default, npm init generates two, ''start'' and ''test''. These can be run with ''npm start'' and ''npm test''. Also, as a bonus point: you can define custom scripts here and can be invoked with '' npm run-script <SCRIPT_NAME>''. Note, that NPM will set up $PATH to look in ''node_modules/.bin'' for executables. This helps avoid global installs of NPM modules.
+Production/staging deployments should be done with environment variables. The most common way to do this is to set the NODE_ENV variable to either production or staging. Depending on your environment variable, you can load your configuration, with modules like ''nconf''. Of course, you can use other environment variables in your Node.js applications with ''process.env'', which is an object that contains the user environment.
+You can use JSCS, which is a code style checker for JS, you can add it:
+<code>
+npm install jscs --save-dev
+</code>
+The very next step you have to make is to enable it from the package.json file by adding a custom script:
+<code>
+scripts: {
+    "jscs": "jscs index.js"
+}
+</code>
+Prefer JS over JSON for configuration files. Something like this:
+<code>
+var url = require('url');
+var config = module.exports = {};
+var redisToGoConfig;
+config.server = {
+  host: '0.0.0.0',
+  port: process.env.PORT || 3000
+};
+// look, a comment in the config file!
+// would be tricky in a JSON ;)
+config.redis = {
+  host: 'localhost',
+  port: 6379,
+  options: {
+  }
+};
+if (process.env.REDISTOGO_URL) {
+  redisToGoConfig = url.parse(process.env.REDISTOGO_URL);
+  config.redis.port = redisToGoConfig.port;
+  config.redis.host = redisToGoConfig.hostname;
+  config.redis.options.auth_pass = redisToGoConfig.auth.split(':')[1];
+}
+</code>

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