Podcast
Questions and Answers
What is the primary reason why ajax(..) function does not return any value to be assigned to the data variable?
What is the primary reason why ajax(..) function does not return any value to be assigned to the data variable?
- Ajax requests are blocked by the browser
- Ajax requests are asynchronous and do not complete synchronously (correct)
- Ajax requests are not supported by modern browsers
- Ajax requests require a callback function to return a value
What is the purpose of a callback function in an Ajax request?
What is the purpose of a callback function in an Ajax request?
- To cancel the request if it takes too long
- To block the browser UI until the response is received
- To wait for the response and then execute a function (correct)
- To send multiple requests at once
Why is it a bad idea to make synchronous Ajax requests?
Why is it a bad idea to make synchronous Ajax requests?
- They lock the browser UI and prevent user interaction (correct)
- They are slower than asynchronous requests
- They are not supported by modern browsers
- They can cause errors in the browser
What is the difference between the 'now' and 'later' code chunks in the example program?
What is the difference between the 'now' and 'later' code chunks in the example program?
What is the purpose of the setTimeout function in the example program?
What is the purpose of the setTimeout function in the example program?
Why is it important to avoid synchronous Ajax requests?
Why is it important to avoid synchronous Ajax requests?
What is the benefit of using asynchronous Ajax requests?
What is the benefit of using asynchronous Ajax requests?
What is the role of the callback function in the Ajax request?
What is the role of the callback function in the Ajax request?
Why is it important to use asynchronous programming in web development?
Why is it important to use asynchronous programming in web development?
What is the main difference between synchronous and asynchronous programming?
What is the main difference between synchronous and asynchronous programming?
Study Notes
Concurrency and Race Conditions
- In JavaScript, the order of function execution is non-deterministic, leading to "race conditions" where the outcome of two functions (e.g.,
foo()andbar()) racing against each other is unpredictable. - A "race condition" occurs when the outcome of multiple functions cannot be reliably predicted.
Concurrency and the Event Loop
- Concurrency in JavaScript involves multiple "processes" executing simultaneously, but not necessarily at the same instant.
- These "processes" are virtual processes or tasks that represent a logically connected, sequential series of operations.
- The event loop is an array that acts as a queue, where events are executed in a first-in, first-out order.
- Each iteration of the event loop is called a "tick," and events are executed in sequence.
Event Loop and setTimeout()
setTimeout()does not put the callback directly on the event loop queue; instead, it sets up a timer that adds the callback to the queue when it expires.- Callbacks wait in line behind existing events in the queue, and there is no way to preempt the queue and skip ahead.
- This explains why
setTimeout()timers may not fire with perfect temporal accuracy.
Asynchronous Programming
- Ajax requests do not complete synchronously, and the
ajax()function does not return a value immediately. - Instead, a callback function is used to handle the response when it is received.
- Asynchronous programming involves breaking up a program into small chunks that execute one after the other in the event loop queue.
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Description
Understand how JavaScript handles function ordering and race conditions, including the concept of run-to-completion behavior and its implications.
