JavaScript Asynchronous Programming
Review JavaScript asynchronous programming with callbacks, promises, and async/await for better code management.
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JavaScript is single-threaded, meaning it can only execute one task at a time in a specific order (synchronously). However, it supports asynchronous programming to handle tasks like fetching data or waiting for a timer without blocking the execution of other code. This allows JavaScript to remain responsive and efficient, even during long-running operations.
Asynchronous programming
Asynchronous programming allows JavaScript to handle tasks without blocking the execution of other operations. This is particularly useful for time-consuming operations, such as fetching data from an API or reading files, as it keeps the application responsive and efficient.
Unlike synchronous programming, where tasks are executed one after another, asynchronous programming allows tasks to run independently. This often results in a nonsequential or nondeterministic execution order, depending on task completion times.
To illustrate this, consider the following example where three tasks with different delays are executed:
setTimeout(() => { console.log("Step 1"); }, 2000); // Executes after 2 secondssetTimeout(() => { console.log("Step 2"); }, 3500); // Executes after 3.5 secondssetTimeout(() => { console.log("Step 3"); }, 1000); // Executes after 1 second
Step 3 is logged first because it has the shortest delay of 1 second. Step 1 follows after 2 seconds. Step 2 appears last, as it has the longest delay of 3.5 seconds.
The key to understanding asynchronous programming is the event loop, which manages tasks in the background while allowing the main thread to continue running.
To work effectively with asynchronous programming, it's essential to understand its core concepts and mechanisms.
Key concepts
DOM events: DOM events are asynchronous actions triggered by user interactions or system events on a webpage, such as clicking a button or resizing the window. Event listeners handle these actions without blocking other code execution, allowing responsive user interfaces.
AJAX (Asynchronous JavaScript and XML): AJAX is a technique for making asynchronous HTTP requests to fetch or send data to a server without reloading the entire webpage. It is commonly used for dynamic web applications and works through APIs like
XMLHttpRequestor modern alternatives likefetch().Call stack: Keeps track of the order in which functions are called and executed. When calling nested functions, the stack keeps track of their order. ...