snappymail/vendors/knockout/src/subscribables/dependencyDetection.js

(() => {

var outerFrames = [],
    currentFrame,
    lastId = 0,

    begin = options => {
        outerFrames.push(currentFrame);
        currentFrame = options;
    },

    end = () => currentFrame = outerFrames.pop();

ko.dependencyDetection = {
    begin: begin,

    end: end,

    registerDependency: subscribable => {
        if (currentFrame) {
            if (!ko.isSubscribable(subscribable))
                throw new Error("Only subscribable things can act as dependencies");
            currentFrame.callback.call(currentFrame.callbackTarget, subscribable,
                subscribable._id || (subscribable._id = ++lastId));
        }
    },

    ignore: (callback, callbackTarget, callbackArgs) => {
        try {
            begin();
            return callback.apply(callbackTarget, callbackArgs || []);
        } finally {
            end();
        }
    },

    getDependenciesCount: () => currentFrame && currentFrame.computed.getDependenciesCount(),

    isInitial: () => currentFrame && currentFrame.isInitial,

    computed: () => currentFrame && currentFrame.computed
};

})();