WIP

東アジアの文字幅 (East Asian Width) の判定

Unicodeの文字が全角で表示されるか半角で表示されるかは東アジアの文字幅特性値がヒントを与えてくれるそうです。（日本語の場合は）この値がNa（狭）、N（中立）、H（半角）だと半角、W（広）、F（全角）、A（曖昧）だと全角として扱うことが推奨されているようです。

Pythonではunicodedataモジュールを使うとこの特性値を取得できますが、JavaScriptにはそのような関数は見当たりません。ですが、Unicode Consortiumが、どの文字がどの東アジアの文字幅を持つかのデータファイルを公開しているので、そこから判定用のコードを機械的に生成できるはずです。

で、以下が実際に生成したコードです。データファイルに、データファイルに出現しない文字はNとなるとあるので、以下ではN以外（F、H、W、Na、A）についてのみチェックを行い、それ以外をNと判定するようにしています。

コメントで指摘された通り、サロゲートペアの判定部分が間違っていたので修正。

function EastAsianWidth(character) {
	var x = character.charCodeAt(0);
	var y = (character.length == 2) ? character.charCodeAt(1) : 0;
	var codePoint = x;
	if ((0xD800 <= x && x <= 0xDBFF) && (0xDC00 <= y && y <= 0xDFFF)) {
		x &= 0x3FF;
		y &= 0x3FF;
		codePoint = (x << 10) | y;
		codePoint += 0x10000;
	}

	if (
	    (0x3000 == codePoint) ||
	    (0xFF01 <= codePoint && codePoint <= 0xFF60) ||
	    (0xFFE0 <= codePoint && codePoint <= 0xFFE6)
	   ) {
		return 'F';
	}
	if (
	    (0x20A9 == codePoint) ||
	    (0xFF61 <= codePoint && codePoint <= 0xFFBE) ||
	    (0xFFC2 <= codePoint && codePoint <= 0xFFC7) ||
	    (0xFFCA <= codePoint && codePoint <= 0xFFCF) ||
	    (0xFFD2 <= codePoint && codePoint <= 0xFFD7) ||
	    (0xFFDA <= codePoint && codePoint <= 0xFFDC) ||
	    (0xFFE8 <= codePoint && codePoint <= 0xFFEE)
	   ) {
		return 'H';
	}
	if (
	    (0x1100 <= codePoint && codePoint <= 0x115F) ||
	    (0x11A3 <= codePoint && codePoint <= 0x11A7) ||
	    (0x11FA <= codePoint && codePoint <= 0x11FF) ||
	    (0x2329 <= codePoint && codePoint <= 0x232A) ||
	    (0x2E80 <= codePoint && codePoint <= 0x2E99) ||
	    (0x2E9B <= codePoint && codePoint <= 0x2EF3) ||
	    (0x2F00 <= codePoint && codePoint <= 0x2FD5) ||
	    (0x2FF0 <= codePoint && codePoint <= 0x2FFB) ||
	    (0x3001 <= codePoint && codePoint <= 0x303E) ||
	    (0x3041 <= codePoint && codePoint <= 0x3096) ||
	    (0x3099 <= codePoint && codePoint <= 0x30FF) ||
	    (0x3105 <= codePoint && codePoint <= 0x312D) ||
	    (0x3131 <= codePoint && codePoint <= 0x318E) ||
	    (0x3190 <= codePoint && codePoint <= 0x31BA) ||
	    (0x31C0 <= codePoint && codePoint <= 0x31E3) ||
	    (0x31F0 <= codePoint && codePoint <= 0x321E) ||
	    (0x3220 <= codePoint && codePoint <= 0x3247) ||
	    (0x3250 <= codePoint && codePoint <= 0x32FE) ||
	    (0x3300 <= codePoint && codePoint <= 0x4DBF) ||
	    (0x4E00 <= codePoint && codePoint <= 0xA48C) ||
	    (0xA490 <= codePoint && codePoint <= 0xA4C6) ||
	    (0xA960 <= codePoint && codePoint <= 0xA97C) ||
	    (0xAC00 <= codePoint && codePoint <= 0xD7A3) ||
	    (0xD7B0 <= codePoint && codePoint <= 0xD7C6) ||
	    (0xD7CB <= codePoint && codePoint <= 0xD7FB) ||
	    (0xF900 <= codePoint && codePoint <= 0xFAFF) ||
	    (0xFE10 <= codePoint && codePoint <= 0xFE19) ||
	    (0xFE30 <= codePoint && codePoint <= 0xFE52) ||
	    (0xFE54 <= codePoint && codePoint <= 0xFE66) ||
	    (0xFE68 <= codePoint && codePoint <= 0xFE6B) ||
	    (0x1B000 <= codePoint && codePoint <= 0x1B001) ||
	    (0x1F200 <= codePoint && codePoint <= 0x1F202) ||
	    (0x1F210 <= codePoint && codePoint <= 0x1F23A) ||
	    (0x1F240 <= codePoint && codePoint <= 0x1F248) ||
	    (0x1F250 <= codePoint && codePoint <= 0x1F251) ||
	    (0x20000 <= codePoint && codePoint <= 0x2F73F) ||
	    (0x2B740 <= codePoint && codePoint <= 0x2FFFD) ||
	    (0x30000 <= codePoint && codePoint <= 0x3FFFD)
	   ) {
		return 'W';
	}
	if (
	    (0x0020 <= codePoint && codePoint <= 0x007E) ||
	    (0x00A2 <= codePoint && codePoint <= 0x00A3) ||
	    (0x00A5 <= codePoint && codePoint <= 0x00A6) ||
	    (0x00AC == codePoint) ||
	    (0x00AF == codePoint) ||
	    (0x27E6 <= codePoint && codePoint <= 0x27ED) ||
	    (0x2985 <= codePoint && codePoint <= 0x2986)
	   ) {
		return 'Na';
	}
	if (
	    (0x00A1 == codePoint) ||
	    (0x00A4 == codePoint) ||
	    (0x00A7 <= codePoint && codePoint <= 0x00A8) ||
	    (0x00AA == codePoint) ||
	    (0x00AD <= codePoint && codePoint <= 0x00AE) ||
	    (0x00B0 <= codePoint && codePoint <= 0x00B4) ||
	    (0x00B6 <= codePoint && codePoint <= 0x00BA) ||
	    (0x00BC <= codePoint && codePoint <= 0x00BF) ||
	    (0x00C6 == codePoint) ||
	    (0x00D0 == codePoint) ||
	    (0x00D7 <= codePoint && codePoint <= 0x00D8) ||
	    (0x00DE <= codePoint && codePoint <= 0x00E1) ||
	    (0x00E6 == codePoint) ||
	    (0x00E8 <= codePoint && codePoint <= 0x00EA) ||
	    (0x00EC <= codePoint && codePoint <= 0x00ED) ||
	    (0x00F0 == codePoint) ||
	    (0x00F2 <= codePoint && codePoint <= 0x00F3) ||
	    (0x00F7 <= codePoint && codePoint <= 0x00FA) ||
	    (0x00FC == codePoint) ||
	    (0x00FE == codePoint) ||
	    (0x0101 == codePoint) ||
	    (0x0111 == codePoint) ||
	    (0x0113 == codePoint) ||
	    (0x011B == codePoint) ||
	    (0x0126 <= codePoint && codePoint <= 0x0127) ||
	    (0x012B == codePoint) ||
	    (0x0131 <= codePoint && codePoint <= 0x0133) ||
	    (0x0138 == codePoint) ||
	    (0x013F <= codePoint && codePoint <= 0x0142) ||
	    (0x0144 == codePoint) ||
	    (0x0148 <= codePoint && codePoint <= 0x014B) ||
	    (0x014D == codePoint) ||
	    (0x0152 <= codePoint && codePoint <= 0x0153) ||
	    (0x0166 <= codePoint && codePoint <= 0x0167) ||
	    (0x016B == codePoint) ||
	    (0x01CE == codePoint) ||
	    (0x01D0 == codePoint) ||
	    (0x01D2 == codePoint) ||
	    (0x01D4 == codePoint) ||
	    (0x01D6 == codePoint) ||
	    (0x01D8 == codePoint) ||
	    (0x01DA == codePoint) ||
	    (0x01DC == codePoint) ||
	    (0x0251 == codePoint) ||
	    (0x0261 == codePoint) ||
	    (0x02C4 == codePoint) ||
	    (0x02C7 == codePoint) ||
	    (0x02C9 <= codePoint && codePoint <= 0x02CB) ||
	    (0x02CD == codePoint) ||
	    (0x02D0 == codePoint) ||
	    (0x02D8 <= codePoint && codePoint <= 0x02DB) ||
	    (0x02DD == codePoint) ||
	    (0x02DF == codePoint) ||
	    (0x0300 <= codePoint && codePoint <= 0x036F) ||
	    (0x0391 <= codePoint && codePoint <= 0x03A1) ||
	    (0x03A3 <= codePoint && codePoint <= 0x03A9) ||
	    (0x03B1 <= codePoint && codePoint <= 0x03C1) ||
	    (0x03C3 <= codePoint && codePoint <= 0x03C9) ||
	    (0x0401 == codePoint) ||
	    (0x0410 <= codePoint && codePoint <= 0x044F) ||
	    (0x0451 == codePoint) ||
	    (0x2010 == codePoint) ||
	    (0x2013 <= codePoint && codePoint <= 0x2016) ||
	    (0x2018 <= codePoint && codePoint <= 0x2019) ||
	    (0x201C <= codePoint && codePoint <= 0x201D) ||
	    (0x2020 <= codePoint && codePoint <= 0x2022) ||
	    (0x2024 <= codePoint && codePoint <= 0x2027) ||
	    (0x2030 == codePoint) ||
	    (0x2032 <= codePoint && codePoint <= 0x2033) ||
	    (0x2035 == codePoint) ||
	    (0x203B == codePoint) ||
	    (0x203E == codePoint) ||
	    (0x2074 == codePoint) ||
	    (0x207F == codePoint) ||
	    (0x2081 <= codePoint && codePoint <= 0x2084) ||
	    (0x20AC == codePoint) ||
	    (0x2103 == codePoint) ||
	    (0x2105 == codePoint) ||
	    (0x2109 == codePoint) ||
	    (0x2113 == codePoint) ||
	    (0x2116 == codePoint) ||
	    (0x2121 <= codePoint && codePoint <= 0x2122) ||
	    (0x2126 == codePoint) ||
	    (0x212B == codePoint) ||
	    (0x2153 <= codePoint && codePoint <= 0x2154) ||
	    (0x215B <= codePoint && codePoint <= 0x215E) ||
	    (0x2160 <= codePoint && codePoint <= 0x216B) ||
	    (0x2170 <= codePoint && codePoint <= 0x2179) ||
	    (0x2189 == codePoint) ||
	    (0x2190 <= codePoint && codePoint <= 0x2199) ||
	    (0x21B8 <= codePoint && codePoint <= 0x21B9) ||
	    (0x21D2 == codePoint) ||
	    (0x21D4 == codePoint) ||
	    (0x21E7 == codePoint) ||
	    (0x2200 == codePoint) ||
	    (0x2202 <= codePoint && codePoint <= 0x2203) ||
	    (0x2207 <= codePoint && codePoint <= 0x2208) ||
	    (0x220B == codePoint) ||
	    (0x220F == codePoint) ||
	    (0x2211 == codePoint) ||
	    (0x2215 == codePoint) ||
	    (0x221A == codePoint) ||
	    (0x221D <= codePoint && codePoint <= 0x2220) ||
	    (0x2223 == codePoint) ||
	    (0x2225 == codePoint) ||
	    (0x2227 <= codePoint && codePoint <= 0x222C) ||
	    (0x222E == codePoint) ||
	    (0x2234 <= codePoint && codePoint <= 0x2237) ||
	    (0x223C <= codePoint && codePoint <= 0x223D) ||
	    (0x2248 == codePoint) ||
	    (0x224C == codePoint) ||
	    (0x2252 == codePoint) ||
	    (0x2260 <= codePoint && codePoint <= 0x2261) ||
	    (0x2264 <= codePoint && codePoint <= 0x2267) ||
	    (0x226A <= codePoint && codePoint <= 0x226B) ||
	    (0x226E <= codePoint && codePoint <= 0x226F) ||
	    (0x2282 <= codePoint && codePoint <= 0x2283) ||
	    (0x2286 <= codePoint && codePoint <= 0x2287) ||
	    (0x2295 == codePoint) ||
	    (0x2299 == codePoint) ||
	    (0x22A5 == codePoint) ||
	    (0x22BF == codePoint) ||
	    (0x2312 == codePoint) ||
	    (0x2460 <= codePoint && codePoint <= 0x24E9) ||
	    (0x24EB <= codePoint && codePoint <= 0x254B) ||
	    (0x2550 <= codePoint && codePoint <= 0x2573) ||
	    (0x2580 <= codePoint && codePoint <= 0x258F) ||
	    (0x2592 <= codePoint && codePoint <= 0x2595) ||
	    (0x25A0 <= codePoint && codePoint <= 0x25A1) ||
	    (0x25A3 <= codePoint && codePoint <= 0x25A9) ||
	    (0x25B2 <= codePoint && codePoint <= 0x25B3) ||
	    (0x25B6 <= codePoint && codePoint <= 0x25B7) ||
	    (0x25BC <= codePoint && codePoint <= 0x25BD) ||
	    (0x25C0 <= codePoint && codePoint <= 0x25C1) ||
	    (0x25C6 <= codePoint && codePoint <= 0x25C8) ||
	    (0x25CB == codePoint) ||
	    (0x25CE <= codePoint && codePoint <= 0x25D1) ||
	    (0x25E2 <= codePoint && codePoint <= 0x25E5) ||
	    (0x25EF == codePoint) ||
	    (0x2605 <= codePoint && codePoint <= 0x2606) ||
	    (0x2609 == codePoint) ||
	    (0x260E <= codePoint && codePoint <= 0x260F) ||
	    (0x2614 <= codePoint && codePoint <= 0x2615) ||
	    (0x261C == codePoint) ||
	    (0x261E == codePoint) ||
	    (0x2640 == codePoint) ||
	    (0x2642 == codePoint) ||
	    (0x2660 <= codePoint && codePoint <= 0x2661) ||
	    (0x2663 <= codePoint && codePoint <= 0x2665) ||
	    (0x2667 <= codePoint && codePoint <= 0x266A) ||
	    (0x266C <= codePoint && codePoint <= 0x266D) ||
	    (0x266F == codePoint) ||
	    (0x269E <= codePoint && codePoint <= 0x269F) ||
	    (0x26BE <= codePoint && codePoint <= 0x26BF) ||
	    (0x26C4 <= codePoint && codePoint <= 0x26CD) ||
	    (0x26CF <= codePoint && codePoint <= 0x26E1) ||
	    (0x26E3 == codePoint) ||
	    (0x26E8 <= codePoint && codePoint <= 0x26FF) ||
	    (0x273D == codePoint) ||
	    (0x2757 == codePoint) ||
	    (0x2776 <= codePoint && codePoint <= 0x277F) ||
	    (0x2B55 <= codePoint && codePoint <= 0x2B59) ||
	    (0x3248 <= codePoint && codePoint <= 0x324F) ||
	    (0xE000 <= codePoint && codePoint <= 0xF8FF) ||
	    (0xFE00 <= codePoint && codePoint <= 0xFE0F) ||
	    (0xFFFD == codePoint) ||
	    (0x1F100 <= codePoint && codePoint <= 0x1F10A) ||
	    (0x1F110 <= codePoint && codePoint <= 0x1F12D) ||
	    (0x1F130 <= codePoint && codePoint <= 0x1F169) ||
	    (0x1F170 <= codePoint && codePoint <= 0x1F19A) ||
	    (0xE0100 <= codePoint && codePoint <= 0xE01EF) ||
	    (0xF0000 <= codePoint && codePoint <= 0xFFFFD) ||
	    (0x100000 <= codePoint && codePoint <= 0x10FFFD)
	   ) {
		return 'A';
	}

	return 'N';
}

参考