base64编码加密解密的JavaScript实现

2018-07-20 来源：open-open
<!doctype html public "-//w3c//dtd html 4.01 transitional//en" "http://www.w3.org/tr/html4/loose.dtd">
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=gb2312">
<title>base64编码加密解密</title>
<script language="javascript">
    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:
                    // 0xxxxxxx
                    out += str.charAt(i - 1);
                    break;
                case 12: case 13:
                    // 110x xxxx   10xx xxxx
                    char2 = str.charCodeAt(i++);
                    out += String.fromCharCode(((c & 0x1f) << 6) | (char2 & 0x3f));
                    break;
                case 14:
                    // 1110 xxxx  10xx xxxx  10xx xxxx
                    char2 = str.charCodeAt(i++);
                    char3 = str.charCodeAt(i++);
                    out += String.fromCharCode(((c & 0x0f) << 12) |
                       ((char2 & 0x3f) << 6) |
                       ((char3 & 0x3f) << 0));
                    break;
            }
        }

        return out;
    }

    function doit() {
        var f = document.f
        f.output.value = base64encode(utf16to8(f.source.value))
        f.decode.value = utf8to16(base64decode(f.output.value))
    }
</script>
</head>
<body style="padding-left:50px;">
<h1 align="center">base64编码加密解密</h1>
<form name="f">
  原码<br>
  <textarea name="source" rows=4 cols=60 wrap="soft"></textarea>
  <br>
  <br>
  base64 encode<br>
  <textarea name="output" rows=4 cols=60 wrap="soft"></textarea>
  <br>
  <br>
  base64 decode<br>
  <textarea name="decode" rows=4 cols=60 wrap="soft"></textarea>
  <br>
  <br>
  <input type=button value="转换" onClick="doit()">
</form>
</body>
</html>
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