What Is Parallelism in JavaScript?
JavaScript can struggle with performance-intensive tasks because it’s a single-threaded language. Using parallelism, it’s possible to achieve multithreaded execution in JavaScript and improve the performance and responsiveness of your modern web apps.
Parallelism in JavaScript Programming
Parallelism is crucial in modern computing for improving performance and scalability. It does this by effectively utilizing available resources.
A common technique used to achieve parallelism in programming is multi-threading. The JavaScript thread, however, is a single-thread system and can only handle one task at a time. This means it is unfamiliar with parallel program executions.
JavaScript Fakes Parallel Programming
A common misconception about parallelism is that it’s possible to achieve it usingasynchronous programming techniqueslike async/await, callbacks, and promises:
These techniques do not actually execute code in parallel. JavaScript uses the event loop to mimic parallel programming within its single-thread design.
The event loop is a fundamental part of the JavaScript runtime environment. It allows you to execute asynchronous operations, such as network requests, in the background without blocking the main single thread.
The event loop constantly checks for new events or tasks in a queue and executes them one by one sequentially. This technique allows JavaScript to achieve concurrency and theoretical parallelism.
Concurrency vs. Parallelism
Concurrency and parallelism are often misunderstood and interchanged in the JavaScript world.
Concurrency in JavaScript refers to the ability to execute multiple tasks by overlapping the execution of the tasks. Where one task can start before another completes, but the tasks can neither start nor end simultaneously. This enables JavaScript to efficiently handle operations,such as fetching data from a REST APIor reading files, without blocking the main execution thread.
Parallelism, on the other hand, refers to the ability to execute multiple tasks simultaneously across multiple threads. These background threads can execute tasks independently and simultaneously. This opens up opportunities for achieving true parallelism in JavaScript applications.
JavaScript’s applications can achieve true parallelism throughthe use of Web Workers.
Web Workers Introduce Parallelism to JavaScript
Web Workers are a feature of modern web browsers that allow JavaScript code to run in background threads, separate from the main execution thread. Unlike the main thread, which handles user interactions and UI updates. The Web Worker would be dedicated to performing computationally intensive tasks.
Below is a diagram representation of the operation of a Web Worker in JavaScript.
The main thread and the Web Worker can communicate using message passing. Using thepostMessagemethod to send messages and theonmessageevent handler to receive messages, you can pass instructions or data back and forth.
Creating a Web Worker
To create a Web Worker, you need to create a separate JavaScript file.
Here is an example:
The above example creates a new Web Worker by passing the path to the worker script (worker.js) as an argument to theWorkerconstructor. you could send a message to the Web Worker using thepostMessagemethod and listen for messages from the Web Worker using theonmessageevent handler.
You should then create the worker script (worker.js) file:
The Web Worker script listens for messages from the main thread using theonmessageevent handler. Upon receiving a message, you log out the message insideevent.dataand send a new message to the main thread with thepostMessagemethod.
Leveraging Parallelism With Web Workers
The primary use case for Web Workers is executing computationally intensive JavaScript tasks in parallel. By offloading these tasks to Web Workers, you may achieve significant performance improvements.
Here is an example of using a web worker to perform a heavy calculation:
Worker.js:
In this example, you pass an array of numbers from the main thread to the Web Worker. The Web Worker performs the computation using the provided array of data and sends the result back to the main thread. TheperformHeavyCalculation()function maps each number to its cube, filters out the even numbers, and finally sums them.
Limitations and Considerations
While Web Workers provide a mechanism for achieving parallelism in JavaScript, it’s important to consider a few limitations and considerations:
Achieve True Parallelism in JavaScript
Parallelism in JavaScript is an exciting concept that enables true concurrent execution of tasks, even in a primarily single-threaded language. With the introduction of Web Workers, you can tap into the power of parallelism and achieve significant performance improvements in your JavaScript applications.
Threading significantly reduces the execution time of a program. Learn how to implement threading in Python.
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