Node JS

Question 1

How does Node.js handle asynchronous operations?

Answer 1

Node.js is asynchronous and operates on a single thread that doesn’t have to wait for operations to complete before starting others. It uses an event queue to manage pending operations.

Question 2

What type of projects is Node.js not suitable for?

Answer 2

Node.js is not suitable for high CPU-intensive projects like image processing, due to its single-threaded nature, which can block the event loop. It is better suited for network-intensive projects.

Question 3

What language and engine is Node.js built on?

Answer 3

Node.js is built on C++ and uses Google’s V8 engine.

Question 4

How do you run a JavaScript file with Node.js?

Answer 4

You can run a JavaScript file with Node.js by typing node <filename> in the terminal.

Question 5

What is the equivalent of global objects in Node.js compared to the browser?

Answer 5

In the browser, global objects like console and setTimeout are prefixed with window (e.g., window.console.log). In Node.js, these objects are prefixed with global (e.g., global.console.log). Variables you define in the global scope are not prefixed.

Question 6

What is the purpose of the main module in a Node.js application?

Answer 6

Every Node.js application has a main module. You can inspect its properties using console.log(module). This helps prevent variable conflicts because each file is a separate module.

Question 7

How can you scan for errors in a Node.js application?

Answer 7

You can use jshint in the terminal to scan for errors in a Node.js application.

Question 8

What does the module wrapper function in Node.js do?

Answer 8

Node.js wraps each module in a function with the signature function (exports, require, module, __filename, __dirname) { … } behind the scenes. This allows for module encapsulation.

Question 9

Is require a global function in Node.js?

Answer 9

require seems like a global function, but it is not. It is provided to each module by the module wrapper function.

Question 10

What is exports in Node.js?

Answer 10

exports is an alias for module.exports and is used to export functions and objects from a module.

Question 11

What are the main phases of the Node.js event loop?

Answer 11

1. Timers: Executes callbacks scheduled by setTimeout() or setInterval().
2. Pending Callbacks: Executes I/O callbacks deferred to the next loop iteration.
3. Idle, Prepare: Used internally by Node.js.
4. Poll: Retrieves new I/O events and executes I/O-related callbacks.
5. Check: Executes setImmediate() callbacks.
6. Close Callbacks: Executes close callbacks, e.g., socket.on(‘close’, …).

Question 12

What is the purpose of the Timers phase in the Node.js event loop?

Answer 12

The Timers phase executes callbacks scheduled by setTimeout() or setInterval().

Question 13

What happens during the Pending Callbacks phase?

Answer 13

I/O callbacks that were deferred to the next loop iteration are executed during this phase.

Question 14

Explain the Poll phase in the Node.js event loop.

Answer 14

The Poll phase is responsible for retrieving new I/O events and executing I/O-related callbacks. It will block if there are no scheduled timers, waiting for I/O events.

Question 15

When are setImmediate() callbacks executed in the Node.js event loop?

Answer 15

setImmediate() callbacks are executed during the Check phase of the event loop.

Question 16

What is the role of the Close Callbacks phase?

Answer 16

The Close Callbacks phase handles the execution of some close callbacks, such as socket.on(‘close’, …).

Question 17

How does the Node.js event loop determine if it should exit or keep running?

Answer 17

Node.js will keep the event loop running as long as there are pending operations (e.g., I/O callbacks, timers, or callbacks in the task queue). It will exit when there are no more operations to perform.

Question 18

What is the function of the setTimeout(0) method in Node.js?

Answer 18

Using setTimeout(0) allows you to schedule a callback to be run after the current call stack is cleared, effectively running it in the next iteration of the event loop.

Question 19

How do worker threads interact with the main thread in Node.js?

Answer 19

Worker threads in Node.js perform operations in the background. The main thread is put to sleep and wakes up when there are events to process, a thread pool thread completes an operation, or the next timer goes off.

Question 20

How does the event loop in Node.js differ from the event loop in the browser?

Answer 20

• Node.js: Utilizes C++ APIs for I/O operations.
• Browser: Utilizes Web APIs for tasks such as AJAX requests and setTimeout.

Question 21

What happens when the event loop’s call stack is empty?

Answer 21

When the call stack is empty, the event loop checks the task queue and pushes the next callback onto the call stack to execute it.

Question 22

Explain the role of web APIs in the browser’s event loop.

Answer 22

The browser uses web APIs (e.g., AJAX, setTimeout) to handle asynchronous operations, allowing the single-threaded JavaScript runtime to offload tasks to these APIs and free up the call stack for other operations.