Best way to count characters in Javascript for a tweet

Question

From the Twitter API docs ( http://dev.twitter.com/pages/counting_characters ):

the 140 chars tweet limit doesn't really count the characters but rather the bytes of the string.

How would I be able to count the bytes in a string using Javascript or does every character in my string always use 2 bytes since I set the encoding of my page to UTF-8?

Perhaps there is already a nice counter function for me to use?

Answer 1

Actually, because of the t.co url shortener, just counting characters doesn't work anymore. Check out these two Twitter references to see how to handle shortened links:

https://support.twitter.com/articles/78124-how-to-shorten-links-urls

https://dev.twitter.com/docs/tco-url-wrapper/how-twitter-wrap-urls

If you're looking for help on the client-side, you'll have to make a new friend with twitter-text.js

https://github.com/twitter/twitter-text-js

I also posted a walk-through of a function I use to count the remaining characters in a tweet

http://blog.pay4tweet.com/2012/04/27/twitter-lifts-140-character-limit/

The function looks like this

function charactersleft(tweet) {
    var url, i, lenUrlArr;
    var virtualTweet = tweet;
    var filler = "01234567890123456789";
    var extractedUrls = twttr.txt.extractUrlsWithIndices(tweet);
    var remaining = 140;
    lenUrlArr = extractedUrls.length;
    if ( lenUrlArr > 0 ) {
        for (var i = 0; i < lenUrlArr; i++) {
            url = extractedUrls[i].url;
            virtualTweet = virtualTweet.replace(url,filler);
        }
    }
    remaining = remaining - virtualTweet.length;
    return remaining;
}

The function returns the number of characters remaining, assuming that all URLs, including those shortened to less than 20 characters, have been "shortened" by t.co to 19 characters plus a space.

It assumes that twitter-text.js is being included.

Answer 2

Thanks moluv00 for your answer that save me some search and put me on the right track. I just wanted to share the way I proceeded to deal with twitter characters counting (due to tiny urls) in my app.

A pull request as been merged on the github repository on 2012-05-31 introducing the twttr.txt.getTweetLength(text, options) function that is taking consideration to t.co URLs and defined as follow :

twttr.txt.getTweetLength = function(text, options) {
    if (!options) {
        options = {
            short_url_length: 22,
            short_url_length_https: 23
        };
    }
    var textLength = text.length;
    var urlsWithIndices = twttr.txt.extractUrlsWithIndices(text);

    for (var i = 0; i < urlsWithIndices.length; i++) {
        // Subtract the length of the original URL
        textLength += urlsWithIndices[i].indices[0] - urlsWithIndices[i].indices[1];

        // Add 21 characters for URL starting with https://
        // Otherwise add 20 characters
        if (urlsWithIndices[i].url.toLowerCase().match(/^https:\/\//)) {
            textLength += options.short_url_length_https;
        } else {
            textLength += options.short_url_length;
        }
    }

    return textLength;
};

So your function will just become :

function charactersleft(tweet) {
    return 140 - twttr.txt.getTweetLength(tweet);
}

Plus, regarding the best practices with t.co we should retrieve the short_url_length and short_url_length_https values from twitter and pass them as the options parameter in the twttr.txt.getTweetLength function :

Request GET help/configuration once daily in your application and cache the "short_url_length" (t.co's current maximum length value) for 24 hours. Cache "short_url_length_https" (the maximum length for HTTPS-based t.co links) and use it as the length of HTTPS-based URLs.

Especially knowing that some changes in the t.co urls length will be effective on 2013-02-20 as described in the twitter developer blog