How to implement a lock?

Question

How could something equivalent to lock in C# be implemented in JavaScript?

So, to explain what I'm thinking a simple use case is:

User clicks button B. B raises an onclick event. If B is in event-state the event waits for B to be in ready-state before propagating. If B is in ready-state, B is locked and is set to event-state, then the event propagates. When the event's propagation is complete, B is set to ready-state.

I could see how something close to this could be done, simply by adding and removing the class ready-state from the button. However, the problem is that a user can click a button twice in a row faster than the variable can be set, so this attempt at a lock will fail in some circumstances.

Does anyone know how to implement a lock that will not fail in JavaScript?

Answer 1

Lock is a questionable idea in JS which is intended to be threadless and not needing concurrency protection. You're looking to combine calls on deferred execution. The pattern I follow for this is the use of callbacks. Something like this:

var functionLock = false;
var functionCallbacks = [];
var lockingFunction = function (callback) {
    if (functionLock) {
        functionCallbacks.push(callback);
    } else {
        $.longRunning(function(response) {
             while(functionCallbacks.length){
                 var thisCallback = functionCallbacks.pop();
                 thisCallback(response);
             }
        });
    }
}

You can also implement this using DOM event listeners or a pubsub solution.