function callback(fn, args, thisArg) {
    if (fn && typeof fn.call === 'function') {
        return fn.apply(thisArg, args);
    }
}
Calls `fn` with the given `args` in the scope defined by `thisArg` and returns the
value returned by `fn`. If `fn` is not a function, this method returns undefined.
@param fn - The function to call.
@param args - The arguments with which `fn` should be called.
@param [thisArg] - The value of `this` provided for the call to `fn`.