js的string变量存储字符串使用的是unicode编码，要保存时必须选择其他编码后进行传输，比如转成utf-8,utf-32等。存储到数据库中为utf-8编码，读取出来如何转换成正确的字符串就成了问题。现在给出解决方案，可以正确支持中文、emoji表情、英文混合的字符串编码互转。
我要评论/**
* created by hdwang on 2019/1/28.
*/
var convertutf8 = (function() {
/**
* unicode string to utf-8
* @param text 字符串
* @returns {*} utf-8编码
*/
function tobytes(text) {
var result = [], i = 0;
text = encodeuri(text);
while (i < text.length) {
var c = text.charcodeat(i++);
// if it is a % sign, encode the following 2 bytes as a hex value
if (c === 37) {
result.push(parseint(text.substr(i, 2), 16))
i += 2;
// otherwise, just the actual byte
} else {
result.push(c)
}
}
return coercearray(result);
}
/**
* utf8 byte to unicode string
* @param utf8bytes
* @returns {string}
*/
function utf8bytetounicodestr(utf8bytes){
var unicodestr ="";
for (var pos = 0; pos < utf8bytes.length;){
var flag= utf8bytes[pos];
var unicode = 0 ;
if ((flag >>>7) === 0 ) {
unicodestr+= string.fromcharcode(utf8bytes[pos]);
pos += 1;
} else if ((flag &0xfc) === 0xfc ){
unicode = (utf8bytes[pos] & 0x3) << 30;
unicode |= (utf8bytes[pos+1] & 0x3f) << 24;
unicode |= (utf8bytes[pos+2] & 0x3f) << 18;
unicode |= (utf8bytes[pos+3] & 0x3f) << 12;
unicode |= (utf8bytes[pos+4] & 0x3f) << 6;
unicode |= (utf8bytes[pos+5] & 0x3f);
unicodestr+= string.fromcodepoint(unicode) ;
pos += 6;
}else if ((flag &0xf8) === 0xf8 ){
unicode = (utf8bytes[pos] & 0x7) << 24;
unicode |= (utf8bytes[pos+1] & 0x3f) << 18;
unicode |= (utf8bytes[pos+2] & 0x3f) << 12;
unicode |= (utf8bytes[pos+3] & 0x3f) << 6;
unicode |= (utf8bytes[pos+4] & 0x3f);
unicodestr+= string.fromcodepoint(unicode) ;
pos += 5;
} else if ((flag &0xf0) === 0xf0 ){
unicode = (utf8bytes[pos] & 0xf) << 18;
unicode |= (utf8bytes[pos+1] & 0x3f) << 12;
unicode |= (utf8bytes[pos+2] & 0x3f) << 6;
unicode |= (utf8bytes[pos+3] & 0x3f);
unicodestr+= string.fromcodepoint(unicode) ;
pos += 4;
} else if ((flag &0xe0) === 0xe0 ){
unicode = (utf8bytes[pos] & 0x1f) << 12;;
unicode |= (utf8bytes[pos+1] & 0x3f) << 6;
unicode |= (utf8bytes[pos+2] & 0x3f);
unicodestr+= string.fromcharcode(unicode) ;
pos += 3;
} else if ((flag &0xc0) === 0xc0 ){ //110
unicode = (utf8bytes[pos] & 0x3f) << 6;
unicode |= (utf8bytes[pos+1] & 0x3f);
unicodestr+= string.fromcharcode(unicode) ;
pos += 2;
} else{
unicodestr+= string.fromcharcode(utf8bytes[pos]);
pos += 1;
}
}
return unicodestr;
}
function checkint(value) {
return (parseint(value) === value);
}
function checkints(arrayish) {
if (!checkint(arrayish.length)) { return false; }
for (var i = 0; i < arrayish.length; i++) {
if (!checkint(arrayish[i]) || arrayish[i] < 0 || arrayish[i] > 255) {
return false;
}
}
return true;
}
function coercearray(arg, copy) {
// arraybuffer view
if (arg.buffer && arg.name === 'uint8array') {
if (copy) {
if (arg.slice) {
arg = arg.slice();
} else {
arg = array.prototype.slice.call(arg);
}
}
return arg;
}
// it's an array; check it is a valid representation of a byte
if (array.isarray(arg)) {
if (!checkints(arg)) {
throw new error('array contains invalid value: ' + arg);
}
return new uint8array(arg);
}
// something else, but behaves like an array (maybe a buffer? arguments?)
if (checkint(arg.length) && checkints(arg)) {
return new uint8array(arg);
}
throw new error('unsupported array-like object');
}
return {
tobytes: tobytes,
frombytes: utf8bytetounicodestr
}
})()
针对emoji的字节字符，占两个unicode字符。使用string.fromcharcode也可以实现，需要进行两次fromcharcode，没有frompointcode方便。下面展示了utf-8的4字节转换为unicode(utf-16)的过程。
//高char10位[一个unicode字符] (2+6+2=10)
unicode = ((utf8bytes[pos] & 0x3)) << 8 |((utf8bytes[pos+1] & 0x3f) << 2) |((utf8bytes[pos+2] >> 4) & 0x03);
//减去1f600中的1，这里减去6个0即可，低位char已经占据10位
unicode = unicode - parseint('1000000',2)
//加上utf-16高char的标识符
unicode = 0xd800 + unicode;
console.log(unicode);
unicodestr += string.fromcharcode(unicode);
//低char10位[一个unicode字符](4+6)
unicode = ((utf8bytes[pos+2] & 0x0f) << 6) | (utf8bytes[pos+3] & 0x3f);
//加上utf-16低char的标识符
unicode = 0xdc00 + unicode;
console.log(unicode);
unicodestr+= string.fromcharcode(unicode);
pos += 4;
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