Question

I don’t get it.
I can’t increment the Tweet-ID …

Here is a demo: http://jsbin.com/idupoq/1/edit

glb = {};
glb.lastTweetId = 0;

getTweets();

function getTweets()
{
    console.info('# LAST ID');
    console.log(glb.lastTweetId);

    console.info('# TEST 1');
    glb.lastTweetId++;
    console.log(glb.lastTweetId);  

    console.info('# TEST 2');
    glb.lastTweetId = glb.lastTweetId+1;
    console.log(glb.lastTweetId);  

    console.info('# TEST 3, OK IS INT BUT PARSE AGAIN ');
    glb.lastTweetId = parseInt(glb.lastTweetId);
    glb.lastTweetId++;
    console.log(glb.lastTweetId);  

    $.getJSON('http://search.twitter.com/search.json?q=%23wwm&since_id='+glb.lastTweetId+'&include_entities=true&result_type=mixed&lang=de&callback=?', function(data, textStatus)
    {
        if(data.results.length > 0)
        {
            glb.lastTweetId = data.results[0]['id'];
        }
        glb.tm= setTimeout('getTweets();',5000);
    });
}

Thanks in advance!

Answer 1

As others have said already, it is because of Number cannot express 271567725082578941. If all you ever want to do to this number is to increase it by one, then the following function should be all you need:

function stringInc(v){
    var digits = v.toString().split('');
    var i = digits.length-1;
    while (digits[i]==9 && i>0){      
      digits[i] = 0;
      i--;
    }
    digits[i] = 1+parseInt(digits[i]);
    return digits.join('');
}

If you expect to want to do something more with the number, then you might be better off using a BigNumber library as suggested by VisioN.

Either way, you should note that you cannot read the tweet id from data.results[0]['id'], because that is interpreted as a Number and rounded to 271567725082578940. You need to use data.results[0]['id_str'].

See updated jsbin here: http://jsbin.com/idupoq/19/. Notice the console is logging the result from the server:

...

"geo":null,
"id":     271580395022217200,
"id_str":"271580395022217216",
"iso_language_code":"de"

...

So the value 271567725082578940 that you have been observing is incorrect as well.