Often in development, you'll come across the term "callback function." These functions run asynchronously, meaning they execute outside the standard, synchronous flow of a program. But what specifically triggers this asynchronous behavior?
In javascript, the syntax of a callback function doesn't indicate asynchrony. Both synchronous and asynchronous callbacks have similar structures.
The only definitive way to determine whether a function invokes a callback synchronously or asynchronously is to consult the documentation. Without documentation, you can also run a simple test to ascertain its behavior.
Javascript fundamentally lacks built-in asynchronicity. To achieve it, developers have two options:
The event loop is a crucial part of javascript's architecture. It's responsible for initiating asynchronous execution and handling events like network I/O. By employing an I/O primitive like select(), the event loop efficiently waits for multiple I/O operations without creating extra threads.
When I/O operations are complete, select() notifies the interpreter. The interpreter then identifies the callback associated with the relevant I/O channel and executes it. This mechanism also underpins the functionality of setTimeout and setInterval.
Modern browsers and Node.js have expanded on the event loop model. They incorporate threads to handle file-based I/O. Upon completion, these threads communicate with the main event loop to trigger appropriate callback executions.
Asynchronous execution is inherent to the event loop and thread-based I/O management. Understanding these underlying mechanisms enhances one's comprehension of asynchronous programming in Javascript and related technologies.
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