snappymail/vendors/knockout/src/utils.domData.js

ko.utils.domData = new (function () {
    let uniqueId = 0,
        dataStoreKeyExpandoPropertyName = "__ko__" + (Date.now()),
        dataStore = new WeakMap();

    return {
        get: (node, key) => (dataStore.get(node) || {})[key],
        set: (node, key, value) => {
            if (dataStore.has(node)) {
                dataStore.get(node)[key] = value;
            } else {
                let dataForNode = {};
                dataForNode[key] = value;
                dataStore.set(node, dataForNode);
            }
            return value;
        },
        getOrSet: function(node, key, value) {
            return this.get(node, key) || this.set(node, key, value);
        },
        clear: node => dataStore.delete(node),

        nextKey: () => (uniqueId++) + dataStoreKeyExpandoPropertyName
    };
})();