js的string變量存儲字符串使用的是unicode編碼，要保存時必須選擇其他編碼后進行傳輸，比如轉成utf-8,utf-32等。存儲到數據庫中為utf-8編碼，讀取出來如何轉換成正確的字符串就成了問題。現在給出解決方案，可以正確支持中文、emoji表情、英文混合的字符串編碼互轉。

/** * Created by hdwang on 2019/1/28. */var convertUtf8 = (function() {  /**   * unicode string to utf-8   * @param text 字符串   * @returns {*} utf-8編碼   */  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  }})()