Filter as a workaround for a $digest loop problem with angular-meteor in custom filters.

fixLoopFilter.js

/*******************************************************************************
 * @author: Dave Gööck<dave@goeoeck.net>
 *
 * This small filter is just a workaround for some problem with angular-meteor.
 *
 * It doesn't really filter any element of the input array but returns a clone
 * of the input. The clone is the same instance for each input configuration.
 * It's not a deep clone. If the input array contains objects, the result array
 * will contain the same instances.
 *
 * Problem:
 * Using custom filters with ngRepeat in templates can cause a digest
 * loop, that's only happening in angular without meteor. So migrating filters
 * can be painful.
 * Described here: http://stackoverflow.com/questions/37602855/custom-filters-produces-infinit-digest-loop-with-angular-meteor
 *
 * Usage:
 * 1. Add this filter to the base module of your project.
 * 2. Use it in your template as the last filter applied in a chain:
 *
 *     ng-repeat="vm.items | customFilter | fixLoopFilter"
 *
 * Drawbacks:
 * This filter can be performance and memory consuming for large input array or
 * objets. It is just meant as a workarount till the issue is fixed or there is
 * a better workaround for this issue.
 *
 * Dependency: CryptoJS.SHA1
 * https://github.com/dandv/meteor-crypto-sha1
 * Install CryptoJS.SHA1 by "meteor add crypto-sha1"
 ******************************************************************************/
.filter('fixLoopFilter', () => {
    // Singleton instanceCache, holding one singleton instance for each input
    // configuration.
    const instanceCache = {};

    // Pass through filter function, creating or filling a clone instance for
    // the given input.
    return (items) => {
        // Hash of the given items array.
        const hash = CryptoJS.SHA1(angular.toJson(items)).toString();
        // Create new result array instance, if there is none in the cache for
        // this input.
        if (!instanceCache[hash]) instanceCache[hash] = [];
        // Clear the cache instance
        instanceCache[hash].length = 0;
        // Fill the instance with the items (maybe Array.map is not the best choice here).
        items.map((item) => {
            instanceCache[hash].push(item);
        });
        // Return cloned data
        return instanceCache[hash];
    };
})