NodeJs

Thread or Event Loop:

In thread, something called the event loop is generated. The role of this loop is to schedule which operations out only thread should be performing at any given point. Step1: Every thing scheduled with setTimeout() and setInterval() will be executed here. Step2: Pending OS tasks are executed, checks for the callbacks that are ready to be called Step3: Pause the execution and wait for new events to occur Step4: Checks if function related to pending timers related to setimmediate() function are ready to be called. Step5: Manage the close events

The program process -

• The program intializes
• Requires all the modules
• Register the call backs
• Start the event loop
• When the event pool encounters a heavy task it pushes the task to the thread pool and the thread pool consist of 4 thread.

NodeJS uses an Event Driven Architecture

RESTFUL API

• works on the client and server - This constraint operates on the concept that the client and the server should be sepearte from each other and allowed to evolve individually
• Stateless - Server is stateless - meaning that calls can made independently of one another, and each call contains all of the data necessary to complete itself successfully. example - Next Page - The client has to remember the current state/page to go to the next page not the server.
• Use Logical Resources
• Resource Bases URL - The API URL must use resource based URL. example - GET /user insead of /getalluser
• HTTP Methods -
• Send data in JSON form

MongoDb errors handled and removed customAPI error from error handler

Cast error

Evaluating the syntax of the data searched in the MongoDB

DB Migrations Notes

• `npm install mysql --save
• 'sudo npm install -g db-migrate sudo npm install db-migrate-mysql --saveCreate following dirs: config migrations Create dev.json, test.json, prod.json in config directory: { "dev": { "host": "***amazonaws.com", "user": "sa", "password": "", "database": "", "driver": "mysql", "multipleStatements": true }, "sql-file": true } Create the first migrationdb-migrate create seed --config ./config/dev.json` Add SQL statements to {up|down}.sql files. Test migration:
• `db-migrate up --config ./config/test.json'
• `db-migrate down --config ./config/test.json' Run the migration in prod:
• `db-migrate up --config ./config/prod.json' db-migrate down --config ./config/prod.json