Event Loop javascript

Kanha Kumar Khatua — Wed, 15 May 2024 17:32:37 +0000

Event Loop:-

The event loop is a mechanism in JavaScript that allows the execution of asynchronous code. It is a single-threaded loop that constantly checks for events and then executes the appropriate callback functions.

Hoisting:-

Hoisting refers to the process where the interpreter appears to move the declaration of function, variables, or classes to the top of their scope, period, and execution of the code.

When JS code runs it creates a global execution context and pushes it into the call stack and after the complete execution of the code it pops out from the call stack.
If any WEB APIs come then it registers the timer web API or Browser after the timer is expired it pushes into the micro-task queue(high priority, Promises, async/await) or call-back queue (setTimeout, setInterval).
Event loop watch the call stack if the call stack is empty then it pushes the task from the micro-task queue or call-back/task queue.

Starvation:-

It happens because in the micro-task queue if one executes and creates another call-back function it continuously happens and the micro-task is not free due to this higher priority, it runs again and again whenever the call stack is free and there is no chance of the call-back queue to run, due to this call-back queue going into starvation.

What is event loop in nodejs ?

Kanha Kumar Khatua — Tue, 01 Aug 2023 10:59:32 +0000

In Node.js, the event loop is a crucial part of its architecture that allows it to handle asynchronous operations efficiently. Understanding the event loop is essential for writing scalable and non-blocking applications in Node.js. Let's break down how the event loop works:

1. Single-Threaded Non-Blocking Model:
Node.js operates on a single-threaded event loop model. Unlike traditional multi-threaded approaches, Node.js uses a single thread to handle all incoming requests and operations. This single thread does not get blocked by I/O operations, making it highly efficient in handling concurrent tasks.
2. Event Loop Phases:
The event loop in Node.js consists of multiple phases, each serving a specific purpose. These phases are executed in a loop, and during each iteration, the event loop performs the following tasks:

a. Timers: This phase executes callbacks scheduled by setTimeout() and setInterval() functions.

b. Pending I/O callbacks: Executes I/O related callbacks (e.g., networking, file system operations) that were deferred during a previous loop iteration.

c. Idle, prepare: These are internal phases, and they are generally not something developers need to be concerned about.

d. Poll: This is the most critical phase where I/O operations are processed. Node.js checks for new I/O events, such as incoming connections or data being available for reading. If there are pending I/O operations, they are executed in this phase. If there are no pending I/O operations, Node.js will wait here.

e. Check: Executes callbacks registered via setImmediate().

f. Close callbacks: Executes cleanup callbacks, such as socket.on('close', ...).

3.Event Loop Flow:
The event loop operates in a continuous loop, following these steps:

Executes any callbacks scheduled by setTimeout() and setInterval() that have met their timer criteria.

Checks for I/O events (networking, file system, etc.) and executes their callbacks.

Executes setImmediate() callbacks.

If there are no more events to process, Node.js waits in the "Poll" phase for new events.

After the "Poll" phase, Node.js performs some additional checks before starting the next loop iteration.

The process repeats, ensuring that the event loop keeps handling new incoming events without blocking.

4. Callbacks Execution:
Callbacks are functions that are registered to be executed when a particular event occurs. For example, when a network request is completed, the corresponding callback is triggered, allowing the application to respond to that event.

5. Async and Non-Blocking:
Node.js is designed to perform I/O operations asynchronously and in a non-blocking manner. When an I/O operation is initiated (e.g., reading from a file, making a network request), Node.js does not wait for the result. Instead, it continues processing other tasks and registers a callback to be executed once the I/O operation is completed.

This event loop architecture enables Node.js to handle a large number of concurrent connections efficiently. Developers can write code that maximizes the use of asynchronous functions and callbacks to prevent blocking operations and take advantage of Node.js's non-blocking capabilities.

DEV Community: Kanha Kumar Khatua

Event Loop javascript

Event Loop:-

Hoisting:-

Starvation:-

What is event loop in nodejs ?