Impossible to compose a lock..

[mikegwhit]

when attempting to compose a release function, e.g. so that re-requesting the lock (if it exists) returns the release function, it fails stating:

TypeError: method is not a function

Example implementation:

        const release = getLock(file);
        let released = false;
        locks[file] = () => {
            if (!released) {
                released = true;
                release();
                delete locks[file];
            }
        };

Suspected cause: you're using function composition so that even with an arrow function, somehow scope is lost and method returns as undefined