javascript实现的base64编码解码

来源：互联网发布：mcu选型软件编辑：程序博客网时间：2024/04/27 04:15

注意：因为Javascript内部的字符串，都以utf-16的形式进行保存，

因此编码的时候，我们首先必须将utf-8的值转成utf-16再编码，解码的时候，则是解码后还需要将utf-16的值转回成utf-8。

var base64encodechars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";var base64decodechars = new Array(-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,-1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1);function base64encode(str) {var out, i, len;var c1, c2, c3;len = str.length;i = 0;out = "";while (i < len) {c1 = str.charCodeAt(i++) & 0xff;if (i == len) {out += base64encodechars.charAt(c1 >> 2);out += base64encodechars.charAt((c1 & 0x3) << 4);out += "==";break;}c2 = str.charCodeAt(i++);if (i == len) {out += base64encodechars.charAt(c1 >> 2);out += base64encodechars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xf0) >> 4));out += base64encodechars.charAt((c2 & 0xf) << 2);out += "=";break;}c3 = str.charCodeAt(i++);out += base64encodechars.charAt(c1 >> 2);out += base64encodechars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xf0) >> 4));out += base64encodechars.charAt(((c2 & 0xf) << 2) | ((c3 & 0xc0) >> 6));out += base64encodechars.charAt(c3 & 0x3f);}return out;}function base64decode(str) {var c1, c2, c3, c4;var i, len, out;len = str.length;i = 0;out = "";while (i < len) {do {c1 = base64decodechars[str.charCodeAt(i++) & 0xff];} while (i < len && c1 == -1);if (c1 == -1)break;do {c2 = base64decodechars[str.charCodeAt(i++) & 0xff];} while (i < len && c2 == -1);if (c2 == -1)break;out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));do {c3 = str.charCodeAt(i++) & 0xff;if (c3 == 61)return out;c3 = base64decodechars[c3];} while (i < len && c3 == -1);if (c3 == -1)break;out += String.fromCharCode(((c2 & 0xf) << 4) | ((c3 & 0x3c) >> 2));do {c4 = str.charCodeAt(i++) & 0xff;if (c4 == 61)return out;c4 = base64decodechars[c4];} while (i < len && c4 == -1);if (c4 == -1)break;out += String.fromCharCode(((c3 & 0x03) << 6) | c4);}return out;}function utf16to8(str) {var out, i, len, c;out = "";len = str.length;for (i = 0; i < len; i++) {c = str.charCodeAt(i);if ((c >= 0x0001) && (c <= 0x007f)) {out += str.charAt(i);} else if (c > 0x07ff) {out += String.fromCharCode(0xe0 | ((c >> 12) & 0x0f));out += String.fromCharCode(0x80 | ((c >> 6) & 0x3f));out += String.fromCharCode(0x80 | ((c >> 0) & 0x3f));} else {out += String.fromCharCode(0xc0 | ((c >> 6) & 0x1f));out += String.fromCharCode(0x80 | ((c >> 0) & 0x3f));}}return out;}function utf8to16(str) {var out, i, len, c;var char2, char3;out = "";len = str.length;i = 0;while (i < len) {c = str.charCodeAt(i++);switch (c >> 4) {case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:// 0xxxxxxxout += str.charAt(i - 1);break;case 12: case 13:// 110x xxxx   10xx xxxxchar2 = str.charCodeAt(i++);out += String.fromCharCode(((c & 0x1f) << 6) | (char2 & 0x3f));break;case 14:// 1110 xxxx  10xx xxxx  10xx xxxxchar2 = str.charCodeAt(i++);char3 = str.charCodeAt(i++);out += String.fromCharCode(((c & 0x0f) << 12) |((char2 & 0x3f) << 6) |((char3 & 0x3f) << 0));break;}}return out;}

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