/* UTF-8 <=> UTF-16 convertion library.
 *
/* Copyright (C) 1999 Masanao Izumo <[email protected]>
 * 2007 Ma Bingyao <[email protected]>
 * Version: 2.1
 * LastModified: Feb 25, 2007
 * This library is free. You can redistribute it and/or modify it.
 */

/*
 * Interfaces:
 * utf8 = utf16to8(utf16);
 * utf16 = utf16to8(utf8);
 */

function utf16to8(str) {
 if (str.match(/^[\x00-\x7f]*$/) != null) {
 return str;
 }
 var out, i, j, len, c, c2;
 out = [];
 len = str.length;
 for (i = 0, j = 0; i < len; i++, j++) {
 c = str.charCodeAt(i);
 if (c <= 0x7f) {
 out[j] = str.charAt(i);
 }
 else if (c <= 0x7ff) {
 out[j] = String.fromCharCode(0xc0 | (c >>> 6),
 0x80 | (c & 0x3f));
 }
 else if (c < 0xd800 || c > 0xdfff) {
 out[j] = String.fromCharCode(0xe0 | (c >>> 12),
 0x80 | ((c >>> 6) & 0x3f),
 0x80 | (c & 0x3f));
 }
 else {
 if (++i < len) {
 c2 = str.charCodeAt(i);
 if (c <= 0xdbff && 0xdc00 <= c2 && c2 <= 0xdfff) {
 c = ((c & 0x03ff) << 10 | (c2 & 0x03ff)) + 0x010000;
 if (0x010000 <= c && c <= 0x10ffff) {
 out[j] = String.fromCharCode(0xf0 | ((c >>> 18) & 0x3f),
 0x80 | ((c >>> 12) & 0x3f),
 0x80 | ((c >>> 6) & 0x3f),
 0x80 | (c & 0x3f));
 }
 else {
 out[j] = '?';
 }
 }
 else {
 i--;
 out[j] = '?';
 }
 }
 else {
 i--;
 out[j] = '?';
 }
 }
 }
 return out.join('');
}

function utf8to16(str) {
 if ((str.match(/^[\x00-\x7f]*$/) != null) ||
 (str.match(/^[\x00-\xff]*$/) == null)) {
 return str;
 }
 var out, i, j, len, c, c2, c3, c4, s;

 out = [];
 len = str.length;
 i = j = 0;
 while (i < len) {
 c = str.charCodeAt(i++);
 switch (c >> 4) { 
 case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:
 // 0xxx xxxx
out[j++] = str.charAt(i - 1);
 break;
 case 12: case 13:
 // 110x xxxx 10xx xxxx
c2 = str.charCodeAt(i++);
 out[j++] = String.fromCharCode(((c & 0x1f) << 6) |
 (c2 & 0x3f));
 break;
 case 14:
 // 1110 xxxx 10xx xxxx 10xx xxxx
c2 = str.charCodeAt(i++);
 c3 = str.charCodeAt(i++);
 out[j++] = String.fromCharCode(((c & 0x0f) << 12) |
 ((c2 & 0x3f) << 6) |
 (c3 & 0x3f));
 break;
 case 15:
 switch (c & 0xf) {
 case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:
 // 1111 0xxx 10xx xxxx 10xx xxxx 10xx xxxx
c2 = str.charCodeAt(i++);
 c3 = str.charCodeAt(i++);
 c4 = str.charCodeAt(i++);
 s = ((c & 0x07) << 18) |
 ((c2 & 0x3f) << 12) |
 ((c3 & 0x3f) << 6) |
 (c4 & 0x3f) - 0x10000;
 if (0 <= s && s <= 0xfffff) {
 out[j] = String.fromCharCode(((s >>> 10) & 0x03ff) | 0xd800,
 (s & 0x03ff) | 0xdc00);
 }
 else {
 out[j] = '?';
 }
 break;
 case 8: case 9: case 10: case 11:
 // 1111 10xx 10xx xxxx 10xx xxxx 10xx xxxx 10xx xxxx
i+=4;
 out[j] = '?';
 break;
 case 12: case 13:
 // 1111 110x 10xx xxxx 10xx xxxx 10xx xxxx 10xx xxxx 10xx xxxx
i+=5;
 out[j] = '?';
 break;
 }
 }
 j++;
 }
 return out.join('');
}

javascript实现上传图片前的预览（TX的面试题） 可以把编码转换成 gb2312编码lib.UTF8toGB2312.js

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