International sms character counter

Question

I found the number of characters / sms using jQuery , but it does not support international characters like Chinese, Japanese, Thai, etc.

var $remaining = $('#remaining'), $messages = $remaining.next(); $('#message').keyup(function(){ var chars = this.value.length, messages = Math.ceil(chars / 160), remaining = messages * 160 - (chars % (messages * 160) || messages * 160); $remaining.text(remaining + ' characters remaining'); $messages.text(messages + ' message(s)'); }); 

Here are some examples of the wrong number of characters:

您好, 請問 你 吃飯 了 嗎 <<11 characters

สวัสดี คุณ กิน หรือ? & L; <17 characters

こ ん に ち は, あ な た は 食 べ て い ま す か か <<18 characters

안녕하세요, 당신 이 먹는 거죠? & L; <17 characters

हैलो, आप खाते ह ैं? & L; <18 characters

Good Zen, are you a lamb? & L; <22 characters

How can I do this work with non-ASCII characters?

Answer 1

You cannot count on "characters" here. According to the SMS article on Wikipedia, SMS uses one of three different encodings (7-bit GSM, 8-bit GSM and UTF-16). So first you need to know / decide which encoding you will use.

If you know that you will always use UTF-16, then you can calculate the number of 16-bit code units that the string will be in. Standard SMS can consist of 70 16-bit code blocks. But this will limit the messages in Latin letters to 70. Therefore, if you want to use the full 160 characters (with 7-bit encoding) or 140 characters (with 8-bit encoding) for Latin characters, you will need to distinguish between three cases.

Example for counting 16-bit UTF-16 code blocks:

 var message = "您好，請問你吃飯了嗎？"; var utf16codeUnits = 0; for (var i = 0, len = message.length; i < len; i++) { utf16codeUnits += message.charCodeAt(i) < 0x10000 ? 1 : 2; } 

By the way, this one will come up with the same amount as you as “wrong”, so you will need to explain why you think they are wrong.

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EDIT

Despite the fact that I have already been accepted, I quickly hacked a function that correctly (as far as I can tell) calculates 7-bit (if possible) GSM signals and UTF-16 SMS messages: http://jsfiddle.net/puKJb /