text: export function base64_encode (str) { // 编码，配合encodeURIComponent使用
    var c1, c2, c3;
    var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
    var i = 0, len = str.length, strin = '';
    while (i < len) {
      c1 = str.charCodeAt(i++) & 0xff;
      if (i == len) {
        strin += base64EncodeChars.charAt(c1 >> 2);
        strin += base64EncodeChars.charAt((c1 & 0x3) << 4);
        strin += "==";
        break;
      }
      c2 = str.charCodeAt(i++);
      if (i == len) {
        strin += base64EncodeChars.charAt(c1 >> 2);
        strin += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));
        strin += base64EncodeChars.charAt((c2 & 0xF) << 2);
        strin += "=";
        break;
      }
      c3 = str.charCodeAt(i++);
      strin += base64EncodeChars.charAt(c1 >> 2);
      strin += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));
      strin += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6));
      strin += base64EncodeChars.charAt(c3 & 0x3F)
    }
    return strin
  }
  
  export function base64_decode (input) { // 解码，配合decodeURIComponent使用
    var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
    var output = "";
    var chr1, chr2, chr3;
    var enc1, enc2, enc3, enc4;
    var i = 0;
    input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");
    while (i < input.length) {
      enc1 = base64EncodeChars.indexOf(input.charAt(i++));
      enc2 = base64EncodeChars.indexOf(input.charAt(i++));
      enc3 = base64EncodeChars.indexOf(input.charAt(i++));
      enc4 = base64EncodeChars.indexOf(input.charAt(i++));
      chr1 = (enc1 << 2) | (enc2 >> 4);
      chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
      chr3 = ((enc3 & 3) << 6) | enc4;
      output = output + String.fromCharCode(chr1);
      if (enc3 != 64) {
        output = output + String.fromCharCode(chr2);
      }
      if (enc4 != 64) {
        output = output + String.fromCharCode(chr3);
      }
    }
    return utf8_decode(output);
  }
  
  
  export function utf8_decode (utftext) { // utf-8解码
    var string = '';
    let i = 0;
    let c = 0;
    let c1 = 0;
    let c2 = 0;
    while (i < utftext.length) {
      c = utftext.charCodeAt(i);
      if (c < 128) {
        string += String.fromCharCode(c);
        i++;
      } else if ((c > 191) && (c < 224)) {
        c1 = utftext.charCodeAt(i + 1);
        string += String.fromCharCode(((c & 31) << 6) | (c1 & 63));
        i += 2;
      } else {
        c1 = utftext.charCodeAt(i + 1);
        c2 = utftext.charCodeAt(i + 2);
        string += String.fromCharCode(((c & 15) << 12) | ((c1 & 63) << 6) | (c2 & 63));
        i += 3;
      }
    }
    return string;
  }
  