Can a simultaneous read/write conflict occur in JavaScript while browsing?

A situation has arisen where I am executing multiple (let's say four) AJAX calls using AngularJS http get, and I desire each call to invoke a callback function that increments a counter. This way, I can track when all four threads have finished.

I am worried because JavaScript lacks constructs like Java's "synchronized" or "volatile" keywords, which could potentially result in race conditions where two threads collide while incrementing the counter, causing some increments to be missed.

For instance, if two threads access the counter simultaneously, both may read the same value (e.g., 100). Subsequently, they both increment the counter (to 101), leading to an overlooked count (101 instead of the expected 102).

While JavaScript is typically single-threaded, there are exceptions to consider.

Could this scenario actually occur in the browser? If so, is there a method to prevent it?

Answer №1

It is impossible for collisions to occur with AJAX calls. Each response from an AJAX call is treated as a separate message in the JavaScript message queue. The JavaScript runtime processes these messages one by one, completing each task before moving on to the next. This means that callbacks are executed sequentially, ensuring that no two messages (such as AJAX responses) are processed simultaneously.

For more information, you can visit: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/EventLoop

Having extensive experience in JavaScript, I can confirm that this is how the process works.

Answer №2

As you rightly pointed out, due to JavaScript's single-threaded nature, the possibility of a scenario involving read/write overlap is very low. The only way JavaScript can be made multi-threaded is by utilizing web workers, which do not share variables and create clones of objects passed as attributes.

UPDATE

Upon further reflection, consider a function called onCounterIncrement that performs operations when a counter increases. If you delay calling this function after incrementing the counter and instead use something like $watch or a timeout function to monitor changes in the counter, there is a risk of missing a change altogether.

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