最近接手的项目，后台返回的字段是base64加密过了，需要前端解密，前端传参的时候取冒号后面的然后再次加密传参
首先呢，可以github下载base64的js文件
下面这个是我已经修改过可以直接在项目中引用的

export default function Base64() {
        // 私钥
        let _keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
        // 加密
        this.encode = function (input) {
                var output = "";
                var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
                var i = 0;
                input = _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 +
                            _keyStr.charAt(enc1) + _keyStr.charAt(enc2) +
                            _keyStr.charAt(enc3) + _keyStr.charAt(enc4);
                }
                return output;
        }
        // 解密
        this.decode =  (input)=> {
                var output = "";
                var chr1, chr2, chr3;
                var enc1, enc2, enc3, enc4;
                var i = 0;
                if (input==undefined||input==null){

                }else {
                        input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");
                        while (i < input.length) {
                                enc1 = _keyStr.indexOf(input.charAt(i++));
                                enc2 = _keyStr.indexOf(input.charAt(i++));
                                enc3 = _keyStr.indexOf(input.charAt(i++));
                                enc4 = _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 = _utf8_decode(output);
                        return output;
                }

        }
        // private method for UTF-8 encoding
        let _utf8_encode =  (string)=> {
                string = string.replace(/\r\n/g,"\n");
                var utftext = "";
                for (var n = 0; n < string.length; n++) {
                        var 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;
        }
        // private method for UTF-8 decoding
        let _utf8_decode = (utftext)=> {
                var string = "";
                var i = 0;
                var c = c1 = c2 = 0;
                var c1 = 0;
                var c2 = 0;
                var c3 = 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;
        }
}

把以上js放在项目中
在用到的页面

import Base64 from "../../../util/base64";
let base64 = new Base64()
let num = base64.encode('123:456')//编码 MTIzOjQ1Ng==
let num1 = base64.decode(num)//解码 '123:456'
let num2 = num1.split(":")[1] //截取冒号后面的字符串  '456'
console.log(num , num1,num2)

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