全角混じりの文字列の桁数を取得する(全角２桁として計算)

s = "あいうえおabcde"

console.log(s.replace(/[\u0100-\uffff]/g,"--").length)

/*
15
 */

上記のコードだと大雑把すぎることがわかりましたので、コメントいただいた内容を反映してみました。

#ノーマルキャラクタ用判定関数の生成
init_UTF8_map = (scope) ->
	nonSurrogatePair = [
	 [0x00A1,0],[0x00A4,0],[0x00AA,0],[0x00C6,0],[0x00D0,0],[0x00E6,0],[0x00F0,0],[0x00FC,0]
	,[0x00FE,0],[0x0101,0],[0x0111,0],[0x0113,0],[0x011B,0],[0x012B,0],[0x0138,0],[0x0144,0]
	,[0x014D,0],[0x016B,0],[0x01CE,0],[0x01D0,0],[0x01D2,0],[0x01D4,0],[0x01D6,0],[0x01D8,0]
	,[0x01DA,0],[0x01DC,0],[0x0251,0],[0x0261,0],[0x02C4,0],[0x02C7,0],[0x02CD,0],[0x02D0,0]
	,[0x02DD,0],[0x02DF,0],[0x0401,0],[0x0451,0],[0x2010,0],[0x2030,0],[0x2035,0],[0x203B,0]
	,[0x203E,0],[0x2074,0],[0x207F,0],[0x20AC,0],[0x2103,0],[0x2105,0],[0x2109,0],[0x2113,0]
	,[0x2116,0],[0x2126,0],[0x212B,0],[0x21D2,0],[0x21D4,0],[0x21E7,0],[0x2200,0],[0x220B,0]
	,[0x220F,0],[0x2211,0],[0x2215,0],[0x221A,0],[0x2223,0],[0x2225,0],[0x222E,0],[0x2248,0]
	,[0x224C,0],[0x2252,0],[0x2295,0],[0x2299,0],[0x22A5,0],[0x22BF,0],[0x2312,0],[0x25CB,0]
	,[0x25EF,0],[0x2609,0],[0x261C,0],[0x261E,0],[0x2640,0],[0x2642,0],[0x266F,0],[0x273D,0]
	,[0x3000,0],[0xFFFD,0]
	,[0x00A7,0x00A8],[0x00AD,0x00AE],[0x00B0,0x00B4],[0x00B6,0x00BA],[0x00BC,0x00BF],[0x00D7,0x00D8]
	,[0x00DE,0x00E1],[0x00E8,0x00EA],[0x00EC,0x00ED],[0x00F2,0x00F3],[0x00F7,0x00FA],[0x0126,0x0127]
	,[0x0131,0x0133],[0x013F,0x0142],[0x0148,0x014B],[0x0152,0x0153],[0x0166,0x0167],[0x02C9,0x02CB]
	,[0x02D8,0x02DB],[0x0300,0x036F],[0x0391,0x03A9],[0x03B1,0x03C1],[0x03C3,0x03C9],[0x0410,0x044F]
	,[0x1100,0x115F],[0x2013,0x2016],[0x2018,0x2019],[0x201C,0x201D],[0x2020,0x2022],[0x2024,0x2027]
	,[0x2032,0x2033],[0x2081,0x2084],[0x2121,0x2122],[0x2153,0x2154],[0x215B,0x215E],[0x2160,0x216B]
	,[0x2170,0x2179],[0x2190,0x2199],[0x21B8,0x21B9],[0x2202,0x2203],[0x2207,0x2208],[0x221D,0x2220]
	,[0x2227,0x222C],[0x2234,0x2237],[0x223C,0x223D],[0x2260,0x2261],[0x2264,0x2267],[0x226A,0x226B]
	,[0x226E,0x226F],[0x2282,0x2283],[0x2286,0x2287],[0x2329,0x232A],[0x2460,0x24E9],[0x24EB,0x254B]
	,[0x2550,0x2573],[0x2580,0x258F],[0x2592,0x2595],[0x25A0,0x25A1],[0x25A3,0x25A9],[0x25B2,0x25B3]
	,[0x25B6,0x25B7],[0x25BC,0x25BD],[0x25C0,0x25C1],[0x25C6,0x25C8],[0x25CE,0x25D1],[0x25E2,0x25E5]
	,[0x2605,0x2606],[0x260E,0x260F],[0x2614,0x2615],[0x2660,0x2661],[0x2663,0x2665],[0x2667,0x266A]
	,[0x266C,0x266D],[0x2776,0x277F],[0x2E80,0x2FFB],[0x3001,0x303E],[0x3041,0x33FF],[0x3400,0x4DB5]
	,[0x4E00,0x9FBB],[0xA000,0xA4C6],[0xAC00,0xD7A3],[0xE000,0xF8FF],[0xF900,0xFAD9],[0xFE00,0xFE0F]
	,[0xFE10,0xFE19],[0xFE30,0xFE6B],[0xFF01,0xFF60],[0xFFE0,0xFFE6]
	]

	surrogatePair = [
	 [0x20000,0x2a6d6] 
	,[0x2a6d7,0x2f7ff]
	,[0x2f800,0x2fa1d]
	,[0x2fa1e,0x2fffd]
	,[0x30000,0x3fffd]
	,[0xe0100,0xe01ef]
	,[0xf0000,0xffffd]
	,[0x100000,0x10fffd]
	]

	# 1文字判定するためのマップ
	singleCharMap = {}
	# 範囲指定マップ
	rangeArray = []

	# 判定処理テーブルの初期化
	nonSurrogatePair.forEach( (v) ->
		if v[1] == 0
			singleCharMap[v[0]] = true 
		else
			rangeArray.push v
	)

	# 判定処理を行う関数を作成
	scope.isWideChar = (code) ->
		if code of singleCharMap
			return true
		for rng in rangeArray
			if rng[0] <= code and code <= rng[1]
				return true
		false

	scope.isSurrogateChar = (code) ->
		for rng in surrogatePair
			if rng[0] <= code and code <= rng[1]
				return true
		false

# 文字列の1文字づつのレングスを配列で返却
getCharCode = (string,scope=window) ->
	counter = 0
	i = 0
	l = string.length
	result = []

	while i < l
		c = string.charCodeAt(i)
		len = 1
		if 0xd800 <= c and c <= 0xd8ff # surrogate pair
			c = 0x10000 + ((c & 0x3ff) << 10) | (string.charCodeAt(i + 1) & 0x3ff)
			len = 2 if scope.isSurrogateChar(c)
			i++
		else
			# normal chars
			len = 2 if scope.isWideChar(c)

		result.push len
		i++
	result

# サロゲートペアの文字を作成
x = 0x20B9F;  #文字コードをセット
x -= 0x10000;
a = Math.floor(x / 0x400);  #Math.floor()で整数値に変換
a += 0xD800;
b = x % 0x400;
b += 0xDC00;
s = String.fromCharCode(a,b);
ss = s + s

# UTF-8有効マップの初期化と判定関数の生成
init_UTF8_map(window)

console.log ss
console.log getCharCode(ss).reduce( (x,y) -> x+y )
console.log getCharCode("あいうえお").reduce( (x,y) -> x+y )

/*
?? 
4 
10 
*/