js实现unicode码字符串与utf8字节数据互转详解

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。

/**
 * 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;

以上所述是小编给大家介绍的js实现unicode码字符串与utf8字节数据互转详解整合，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对脚本之家网站的支持！