NodeJS Flashcards

Question

What is the difference between asynchronous vs non-blocking?

Answer 1

Asynchronous For a message sent, we will not receive a response immediately An acknowledgement is received when the action is performed - improves performance and efficiency Non-blocking Does not stop/block any operations - receives a response immediately with whatever data is available If no data available, it returns an error Mostly used with I/O operations

Answer 2

process.nextTick() Postpones execution until next iteration of the Event Loop and calls the callback once Event Loop’s current execution is complete setImmediate() Executes a callback on the next iteration of the Event Loop and returns control to the Event Loop for any I/O operations

Answer 3

Environment variable made popular by the express framework When the node application is run, it can check the value of the environment variable and do different things based on it ie. use caching for production, not for development

Answer 4

Buffer Storage of raw data Stream Objects that enable you to read/write data continuously Types: - Readable - reading operations - Writable - writing operations - Duplex - read/write operations - Transform - type of duplex stream where output is computed based on input

Answer 5

Each type of stream is an EventEmitter instance which fires different events at different times Events: - Data - fired when data is available to read - End - fired when no more data to read - Error - fired when it encounters an error - Finish - fired when all data has been flushes

Answer 6

Give instructions to Node.js about which part of the code should be exported from a given file to be shared with other files Encapsulates similar functions in a file and improves project structure

Answer 7

Contains the metadata relevant to the project including project dependencies

Answer 8

- Global resources - Closures - Caching - Promises

Answer 9

Occurs when your app runs out of memory - when default memory allocated to the program has exceeded during execution Resolved by increasing the default memory allocated by using a node CLI command node --max-old-space-size=

Answer 10

Order in which instructions in your program are executed Code is executed sequentially unless it runs across structures that change the control flow ie. loops/conditionals Since I/O operations in Node.js are non-blocking, control flow cannot be linear - registers a callback to the Event Loop and passes control back to the node so it can continue with the flow

Answer 11

A mechanism to connect the output of one stream to another stream creating a chain of stream operations Normally used with piping operations

Answer 12

setTimeout() Implement delays in code execution setInterval() Executes code blocks multiple times process.nextTick() Postpones execution until next iteration of the Event Loop and calls the callback once Event Loop’s current execution is complete setImmediate() Executes a callback on the next iteration of the Event Loop and returns control to the Event Loop for any I/O operations

Answer 13

Pattern for non-blocking I/O operations commonly used in event-driven architecture Consist of 2 components: - Reactor - dispatches I/O event to appropriate handlers - Handler - handles the event

Answer 14

Controlled set of changes to modify data in a db and prevent data loss Help transition the db from current state to a new, desired state

Answer 15

SQL builder with built-in migration framework Keeps track of executed migration scripts and rolls back unsuccessful migrations if needed

Answer 16

Ensures server logic is encapsulated and decoupling from application logic Allows for reusability and increases scalability app. js file - Contains business logic and its execution - Contains access to db and models - Consist of 2 main components - routes and controllers server. js file - Setting up server, port and routes - Initialisation of middleware

Answer 17

Pattern used across async methods in Node.js

Answer 18

Node.js is a single-threaded language and uses multiple threads in the background to execute async code which is not exposed to the developer Node.js provides 2 methods to execute code in parallel to the Event Loop: - child_process module: gives node the ability to run child processes by accessing OS commands - worker_threads module: useful for performing CPU-intensive operations

Answer 19

Two ways to resolve unhandled exceptions: - Using a try/catch block - Using the process object Using a try/catch block will not work for asynchronously thrown errors (ie. errors thrown in a setTimeout()) but can be caught using process.on(“uncaughtException”, callback) as it is always listening to events

Answer 20

Long Term Support LTS versions of Node.js are supported for 18 months and is focused on stability and security making it a better choice for production Current release versions have a shorter lifespan and more frequent updates to the code

Answer 21

Automate the security audit of your dependencies Security audit options: - Snyk - npm outdated - npm audit

Answer 22

Express Mimimal web framework Lodash Utility library Date-fns Helps with parsing, formatting dates Nodemon Used in development to watch for changed files and automatically restarts the node app Winston Logging library

Answer 23

Provides a way of testing expressions If expression evaluates to 0 of false, then the program is terminated

NodeJS Flashcards

(48 cards)