JavaScript 程序：将字符串编码为 Base64

要理解这个示例，你应该了解以下JavaScript编程主题的知识：

• JavaScript字符串

Base64是一组二进制到文本的编码方案，通过将二进制数据翻译成基数为64的ASCII字符串格式来表示。

示例1：使用btoa()将字符串编码为Base64

// 将字符串编码为Base64的程序
// 定义字符串
const str = "Learning JavaScript";

// 编码字符串
const result = window.btoa(str);
console.log(result);

// 解码字符串
const result1 = window.atob(result);
console.log(result1);

输出

TGVhcm5pbmcgSmF2YVNjcmlwdA==
Learning JavaScript

在上述示例中，使用了btoa()方法将字符串转换为Base64。

使用了atob()方法将Base64转换为字符串。

示例2：使用Base64对象将字符串编码为Base64

// 将字符串编码为Base64的程序
// 创建Base64对象
const Base64 = {
  // 私有属性
  _keyStr: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",

  // 编码的公共方法
  encode: function (input) {
    let output = "";
    let chr1, chr2, chr3, enc1, enc2, enc3, enc4;
    let i = 0;

    input = Base64._utf8_encode(input);

    while (i < input.length) {
      chr1 = input.charCodeAt(i++);
      chr2 = input.charCodeAt(i++);
      chr3 = input.charCodeAt(i++);

      enc1 = chr1 >> 2;
      enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
      enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
      enc4 = chr3 & 63;

      if (isNaN(chr2)) {
        enc3 = enc4 = 64;
      } else if (isNaN(chr3)) {
        enc4 = 64;
      }

      output =
        output +
        Base64._keyStr.charAt(enc1) +
        Base64._keyStr.charAt(enc2) +
        Base64._keyStr.charAt(enc3) +
        Base64._keyStr.charAt(enc4);
    }

    return output;
  },

  // 解码的公共方法
  decode: function (input) {
    let output = "";
    let chr1, chr2, chr3;
    let enc1, enc2, enc3, enc4;
    let i = 0;

    input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");

    while (i < input.length) {
      enc1 = Base64._keyStr.indexOf(input.charAt(i++));
      enc2 = Base64._keyStr.indexOf(input.charAt(i++));
      enc3 = Base64._keyStr.indexOf(input.charAt(i++));
      enc4 = Base64._keyStr.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);
      }
    }

    output = Base64._utf8_decode(output);

    return output;
  },

  // UTF-8编码的私有方法
  _utf8_encode: function (string) {
    string = string.replace(/\r\n/g, "\n");
    let utftext = "";

    for (let n = 0; n < string.length; n++) {
      let c = string.charCodeAt(n);

      if (c < 128) {
        utftext += String.fromCharCode(c);
      } else if (c > 127 && c < 2048) {
        utftext += String.fromCharCode((c >> 6) | 192);
        utftext += String.fromCharCode((c & 63) | 128);
      } else {
        utftext += String.fromCharCode((c >> 12) | 224);
        utftext += String.fromCharCode(((c >> 6) & 63) | 128);
        utftext += String.fromCharCode((c & 63) | 128);
      }
    }

    return utftext;
  },

  // UTF-8解码的私有方法
  _utf8_decode: function (utftext) {
    let string = "";
    let i = 0;
    let c = (c1 = c2 = 0);

    while (i < utftext.length) {
      c = utftext.charCodeAt(i);

      if (c < 128) {
        string += String.fromCharCode(c);
        i++;
      } else if (c > 191 && c < 224) {
        c2 = utftext.charCodeAt(i + 1);
        string += String.fromCharCode(((c & 31) << 6) | (c2 & 63));
        i += 2;
      } else {
        c2 = utftext.charCodeAt(i + 1);
        c3 = utftext.charCodeAt(i + 2);
        string += String.fromCharCode(
          ((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63),
        );
        i += 3;
      }
    }
    return string;
  },
};

// 定义字符串
const string = "Learning JavaScript";

// 编码字符串
const encodedString = Base64.encode(string);
console.log(encodedString);

// 解码字符串
const decodedString = Base64.decode(encodedString);
console.log(decodedString);

输出

TGVhcm5pbmcgSmF2YVNjcmlwdA==
Learning JavaScript.

encode()方法将字符串编码为Base64。decode()方法将Base64解码为字符串。