Collection pager

collection-pager.js

// In-progress experiments with this idea before making a proper module

var State = require('ampersand-state');


module.exports = State.extend({
    props: {
        max: ['number', true, 20],
        reverse: 'boolean',
        first: 'any',  // string or bool (true means end-of-collection, false means start-of-collection)
        last: 'string',
        firstIndex: 'string',
        count: 'number'
    },

    initialize: function (spec) {
        this.collection = spec.collection;
        this.pageFetch = spec.fetch;
    },
    
    next: function () {
        if (this.reverse) {
            this._fetch({
                max: this.max,
                before: this.first || true
            });
        } else {
            this._fetch({
                max: this.max,
                after: this.last
            });
        }
    },

    prev: function () {
        if (this.reverse) {
            this._fetch({
                max: this.max,
                after: this.last
            });
        } else {
            this._fetch({
                max: this.max,
                before: this.first
            });
        }
    },

    getPage: function (startingIndex) {
        this._fetch({
            max: this.max,
            index: startingIndex
        });
    },

    getCount: function () {
        this._fetch({
            max: 0
        });
    },

    _fetch: function (opts) {
        var self = this;
        this.pageFetch(opts, function (err, res) {
            if (err) {
                return self.trigger('error', self, err);
            }
            self.update(res.paging);
            var method = res.reset ? 'reset' : 'set';
            self.collection[method](res.items);
        });
    }
});

self.collection.reset(res.items); – I'd leave a choice whether to reset collection or just add items to it to a user. This way it could be easily reused as infinite scrolling module as well.