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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 purpose of a callback function in an Ajax request?
Why is it a bad idea to make synchronous Ajax requests?
What is the difference between the 'now' and 'later' code chunks in the example program?
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What is the purpose of the setTimeout function in the example program?
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Why is it important to avoid synchronous Ajax requests?
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What is the benefit of using asynchronous Ajax requests?
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What is the role of the callback function in the Ajax request?
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Why is it important to use asynchronous programming in web development?
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What is the main difference between synchronous and asynchronous programming?
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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.
