Javascript not parsing large number in JSON correctly

Question

I'm passing back a list of approved tweets from a webserver in JSON format. When I go to the URL: http://localhost:8000/showtweets/?after_id=354210796420608003 in my browser I get the following JSON:

   [{
    "date": "2013-07-08T12:10:09",
    "text": "#RaspberryPi ist auf dem Weg :-)",
    "author_pic_url": "http://a0.twimg.com/profile_images/1315863231/twitter_normal.jpg",
    "id": 354210796420608004,
    "author": "switol"
}]

Which has an id of: 354210796420608004.

When I make a GET call from Javascript, the number changes:

function TweetUpdater() {
}

TweetUpdater.latest_id = 0;
TweetUpdater.undisplayed_tweets = new Array();

TweetUpdater.prototype.get_more_tweets = function () {
    // var since_id = parseFloat(TweetUpdater.get_latestlatest_id;
    // alert(since_id);
    var get_tweets_url = "/showtweets/?after_id="+TweetUpdater.latest_id;
    $.get(get_tweets_url, function (tweets) {
        if (tweets.length > 0) {

            /////////////////////////////////////////////////////////
            alert(tweets[0].id+", "+ tweets[0].text); <<<<< THIS LINE
            /////////////////////////////////////////////////////////

            TweetUpdater.latest_id = tweets[0].id;
            for (var i = 0; i < tweets.length; i++) {
                TweetUpdater.undisplayed_tweets.push(tweets[i]);
            }
        }
    }, "json");
};

This code alerts: 354210796420608000, #RaspberryPi ist auf dem Weg :-)

354210796420608004 != 354210796420608000

Very odd.

Answer 1

No, not very odd. JS represents all numbers as double, and with growing integers you loose precision at some point. See What is JavaScript's highest integer value that a Number can go to without losing precision? for details.

To solve the problem, simply make the id a string - you're not doing calculations with it anyway. You'll have to do that in the original JSON though, otherwise the precision loss happens at JSON.parse already.