Are Mutexes needed in javascript?

Question

I have seen this link: Implementing Mutual Exclusion in JavaScript. On the other hand, I have read that there are no threads in javascript, but what exactly does that mean?

Answer 1

As @william points out,

you may need a mutex if your code does something where it expects a value not to change between when the asynchronous event was fired and when the callback was called.

This can be generalised further - if your code does something where it expects exclusive control of a resource until an asynchronous request resolves, you may need a mutex.

A simple example is where you have a button that fires an ajax call to create a record in the back end. You might need a bit of code to protect you from trigger happy users clicking away and thereby creating multiple records. there are a number of approaches to this problem (e.g. disable the button, enable on ajax success). You could also use a simple lock:

var save_lock = false;
$('#save_button').click(function(){
    if(!save_lock){
        //lock
        save_lock=true;
        $.ajax({
            success:function()
                //unlock
                save_lock = false;  
            }
        });
    }
}

I'm not sure if that's the best approach and I would be interested to see how others handle mutual exclusion in javascript, but as far as i'm aware that's a simple mutex and it is handy.