A Simple Paginator

A Simple Paginator that works without priorities.

by Firebase

HTML

<script src="http://static.firebase.com/v0/firebase.js"></script>
<h3>A Simple Paginator</h3>

<div></div>
<button id="prev">prev 5</button>
<button id="next">next 5</button>

CSS

div {
    padding: 20px;
    font-size: 20px;
    border-radius: 15px;
    background-color: #fafafa;
    border: 1px solid #999;
    font-family:'Courier New', 'Courier', monospaced;
    margin-bottom: 10px;
}
h3 {
    clear: both;
    padding-top: 20px;
}
button {
    font-size: 36px;
}
}

JavaScript

/***************************
  A SIMPLE PAGINATOR
  *************************/
function Paginator(ref, limit) {
    this.ref = ref;
    this.pageNumber = 0;
    this.limit = limit;
    this.lastPageNumber = null;
    this.currentSet = {};
}

Paginator.prototype = {
    nextPage: function (callback) {
        if( this.isLastPage() ) {
            callback(this.currentSet);    
        }
        else {
            var lastKey = getLastKey(this.currentSet);
            // if there is no last key, we need to use undefined as priority
            var pri = lastKey ? null : undefined;
            this.ref.startAt(pri, lastKey)
                .limit(this.limit + (lastKey? 1 : 0))
                .once('value', this._process.bind(this, {
                    cb: callback,
                    dir: 'next',
                    key: lastKey
                }));
        }
    },

    prevPage: function (callback) {
        console.log('prevPage', this.isFirstPage(), this.pageNumber);
        if( this.isFirstPage() ) {
            callback(this.currentSet);    
        }
        else {
            var firstKey = getFirstKey(this.currentSet);
            // if there is no last key, we need to use undefined as priority
            this.ref.endAt(null, firstKey)
                .limit(this.limit+1)
                .once('value', this._process.bind(this, {
                    cb: callback,
                    dir: 'prev',
                    key: firstKey
                }));
        }
    },

    isFirstPage: function () {
        return this.pageNumber === 1;
    },

    isLastPage: function () {
        return this.pageNumber === this.lastPageNumber;
    },

    _process: function (opts, snap) {
        var vals = snap.val(), len = size(vals);
        console.log('_process', opts, len, this.pageNumber, vals);
        if( len < this.limit ) {
            // if the next page returned some results, it becomes the last page
            // otherwise this one is
           ...