Javascript – safe grauding constructor from global this

function Socket() {
if (!(this instanceof Socket)) return new Socket();

this.port = 100;
this.address = ’19.68.10.1′;
}

nodejs – A way to handle connection error in client side – ECONNREFUSED and ETIMEDOUT

ECONNREFUSED – “Could not contact DNS servers”
ETIMEDOUT – “Timeout while contacting DNS servers / Connecting to service”

While ECONNREFUSED error will be thrown quickly upon trying create a tcp connection, ETIMEDOUT will be thrown after a default timeout period (roughly 5 minutes – measured in my code). Currently I am looking for a way to reduce this long wait before ETIMEDOUT happens. Will post soon.

Current leads…

http://stackoverflow.com/questions/3586760/how-do-i-set-a-timeout-for-client-http-connections-in-node-js

socket.setTimeout(2 * 60 * 1000); // 2 minute timeout
socket.addListener(‘timeout’, function() {
socket.destroy();
});

mongodb driver for node.js

https://github.com/christkv/node-mongodb-native – one of the widely used mongodb driver in node.js

Using the driver straight-way results in lot of chained callbacks and will be difficult to manage the code.

 

mongojs is a very nice wrapper around the driver that brings us the mongo shell like syntax to node.js.

https://github.com/gett/mongojs

mongojs – how to generate an object id ?

Use db.bson.ObjectID.createPk()

It will generate a unique object id and returns for our use.

It is an alias for mongodb-native driver’s db.bson_serializer.ObjectID.createPk()

mongojs – get last insert id

db.contacts.insert( { ‘name’ : ‘Jayyy V’, ‘gravatar’ : ‘jayyy0v’ } , cbResult );

function cbResult(err, doc) {
if (err) throw err;
else console.log(doc._id);
}

Creating custom error / extending error type in node.js

/**

• A custom error type to indicate an error message for an app user
• @param message
• @returns {UserError}

*/
function UserError(message) {
  Error.call(this); //super constructor
  Error.captureStackTrace(this, this.constructor); //super helper method to include stack trace in error object

  this.name = this.constructor.name; //set our function’s name as error name.
  this.message = message; //set the error message

} UserError.prototype.__proto__ = Error.prototype;

Correct way to throw an error in node.js

Wrong way - stack trace will not be available

throw “invalid credentials”;

output
node.js:201
throw e; // process.nextTick error, or ‘error’ event on first tick
^
invalid credentials

Correct way – stack trace will be available

throw new Error(“invalid credentials”);

output
node.js:201
throw e; // process.nextTick error, or ‘error’ event on first tick
^
Error: invalid credentials
at Object. (/home/workspace/node/test_exception.js:4:7)
at Module._compile (module.js:432:26)
at Object..js (module.js:450:10)
at Module.load (module.js:351:31)
at Function._load (module.js:310:12)
at Array.0 (module.js:470:10)
at EventEmitter._tickCallback (node.js:192:40)

Calculating the size of a mongo db document and collection

Single Document
mongo shell provides Object.bsonsize() function to calculate the size of a document. Query the relevant document and pass it to this function.

usage

> Object.bsonsize(db.foo.findOne())
622 – output is the size in bytes

All Collections

> use <dbname>
> db.printCollectionStats()

It displays a lot metrics about each of the available collections. And “size” is one of the metric.

foo
{
“ns” : “mydb.foo”,
“count” : 21,
  “size” : 4976,
“storageSize” : 15616,
“numExtents” : 1,
“nindexes” : 1,
“lastExtentSize” : 15616,
“paddingFactor” : 1,
“flags” : 1,
“totalIndexSize” : 8192,
“indexSizes” : {
“_id_” : 8192
},
“ok” : 1
}

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exports vs module.exports in node.js

Here is an example of exporting a mongojs db connection from a module.

db.js
var DBConn = {
URL:’localhost:27017/mydb’
};

var collections = ['posts', 'users'];
var mydb = require(‘mongojs’).connect(DBConn.URL, collections);

module.exports = mydb;

somfile.js
var db = require(‘./db.js’);   //Be sure to mention the correct relative path of db.js file. This code assumes it is in the same dir as somefile.js

db.posts.find(function(err, docs) {
console.log(docs);
});

exports vs module.exports

Although, node.js documentation says exports & module.exports are same, it is same only when you augment it.

eg. module.exports.db = mydb;    or  exports.db = mydb;

Now the module.exports object will look like {db:mydb} . When there is just one API/Object to be exported, doing it this way will result in a boilerplate code wherever the module is required.

require(‘./db.js’).db

To avoid this boilerplate, set the exports object to the required API/Object directly. This can be done only through module.exports

eg. module.exports = mydb;    or   exports = mydb;   //will not work