MongoDB JavaScript function that will return an array of all records matching specified criteria, searching across all collections in the current database. Original from https://stackoverflow.com/a/32790853/1847657

findAll.js

/**
 * Find into all collections.
 * 
 * @param {{}} query
 * @param {[]} fields
 * @param {{}} sort
 * 
 * @return {Array}
 */
function findAll(query, fields, sort) {
    var result = [];
    var collectionNames = db.getCollectionNames();

    collectionNames.forEach(function (collectionName) {
        if (collectionName === 'system.indexes') {
            return;
        }

        db[collectionName]
            .find(query || {}, fields || [])
            .sort(sort || {})
            .forEach(function (doc) {
                result.push(doc);
            })
        ;
    });

    return result;
}