在window对象下有两个api,可以对ASCII编码进行编译,得到base64位的字符串

1. btoa:编码为base64
2. atob:解码为ASCII码

此种方法不能对中文进行操作,因为ASCII码中没有中文,如果编码会得到乱码

要编码中文可以先用encodeURIComponent() 对字符串进行转义,转义后再btoa()成base64就可以,
用atob()解码后再调用decodeURIComponent()得到原来的字符

兼容性:不兼容ie9及以下老版本

兼容ie9以下需要自己封装:
参考>> js设置一个字符串为base64格式

var Base64 = {// private property
_keyStr : "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",// public method for encoding
encode : function (input) {var output = "";var chr1, chr2, chr3, enc1, enc2, enc3, enc4;var 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 +this._keyStr.charAt(enc1) + this._keyStr.charAt(enc2) +this._keyStr.charAt(enc3) + this._keyStr.charAt(enc4);}return output;
},// public method for decoding
decode : function (input) {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 = this._keyStr.indexOf(input.charAt(i++));enc2 = this._keyStr.indexOf(input.charAt(i++));enc3 = this._keyStr.indexOf(input.charAt(i++));enc4 = this._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;},// private method for UTF-8 encoding
_utf8_encode : function (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
_utf8_decode : function (utftext) {var string = "";var i = 0;var 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;
}}

完