JavaScript 长字符串缩短和还原，长度预计能缩短50%以上

用于 uniapp、微信小程序的WebView PostMessage传数据

npm i lz-string


const LZString = require("lz-string")
var string ='UEsDBAoAAAAIAA48LVU9cySLbAEAAJoFAAATAAAAW0NvbnRlbnRfVH';
console.log("样本大小为：" + string.length); //参考：字符长度 20000
var compressed = LZString.compress(string);
console.log(compressed)
console.log("压缩样本的大小为：" + compressed.length); //参考：压缩后字符长度 9800
string = LZString.decompress(compressed);
console.log("Sample is：" + string);      

/* *
   * 压缩字符串
   */
  function compress(strNormalString) {
    console.log(" 压缩前长度： " + strNormalString.length);
    var strCompressedString = "";
    var ht = new Array();
    for (i = 0; i < 128; i++) {
      ht[i] = i;
    }

    var used = 128;
    var intLeftOver = 0;
    var intOutputCode = 0;
    var pcode = 0;
    var ccode = 0;
    var k = 0;

    for (var i = 0; i < strNormalString.length; i++) {
      ccode = strNormalString.charCodeAt(i);
      k = (pcode << 8) | ccode;
      if (ht[k] != null) {
        pcode = ht[k];
      } else {
        intLeftOver += 12;
        intOutputCode <<= 12;
        intOutputCode |= pcode;
        pcode = ccode;
        if (intLeftOver >= 16) {
          strCompressedString += String.fromCharCode(intOutputCode >> (intLeftOver - 16));
          intOutputCode &= (Math.pow(2, (intLeftOver - 16)) - 1);
          intLeftOver -= 16;
        }
        if (used < 4096) {
          used++;
          ht[k] = used - 1;
        }
      }
    }

    if (pcode != 0) {
      intLeftOver += 12;
      intOutputCode <<= 12;
      intOutputCode |= pcode;
    }

    if (intLeftOver >= 16) {
      strCompressedString += String.fromCharCode(intOutputCode >> (intLeftOver - 16));
      intOutputCode &= (Math.pow(2, (intLeftOver - 16)) - 1);
      intLeftOver -= 16;
    }

    if (intLeftOver > 0) {
      intOutputCode <<= (16 - intLeftOver);
      strCompressedString += String.fromCharCode(intOutputCode);
    }

    console.log(strCompressedString + " 压缩后长度： " + strCompressedString.length);
    return strCompressedString;
  }

  /* *
   * 解压缩字符串
   */
  function decompress(strCompressedString) {
    var strNormalString = "";
    var ht = new Array();

    for (i = 0; i < 128; i++) {
      ht[i] = String.fromCharCode(i);
    }

    var used = 128;
    var intLeftOver = 0;
    var intOutputCode = 0;
    var ccode = 0;
    var pcode = 0;
    var key = 0;

    for (var i = 0; i < strCompressedString.length; i++) {
      intLeftOver += 16;
      intOutputCode <<= 16;
      intOutputCode |= strCompressedString.charCodeAt(i);

      while (1) {
        if (intLeftOver >= 12) {
          ccode = intOutputCode >> (intLeftOver - 12);
          if (typeof(key = ht[ccode]) != "undefined") {
            strNormalString += key;
            if (used > 128) {
              ht[ht.length] = ht[pcode] + key.substr(0, 1);
            }
            pcode = ccode;
          } else {
            key = ht[pcode] + ht[pcode].substr(0, 1);
            strNormalString += key;
            ht[ht.length] = ht[pcode] + key.substr(0, 1);
            pcode = ht.length - 1;
          }

          used++;
          intLeftOver -= 12;
          intOutputCode &= (Math.pow(2, intLeftOver) - 1);
        } else {
          break;
        }
      }
    }
    console.log("解压缩后长度：" + strNormalString.length);
    return strNormalString;
  }