How can you encode a string to Base64 in JavaScript?

Question

I have a PHP script that can encode a PNG image to a Base64 string.

I'd like to do the same thing using JavaScript. I know how to open files, but I'm not sure how to do the encoding. I'm not used to working with binary data.

Answer 1

From here:

/** * *  Base64 encode / decode *  http://www.webtoolkit.info/ * **/ 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;     } } 

Also, search for "JavaScript base64 encoding" turns up a lot of other options, and the above was the first one.

Answer 2

You can use btoa() and atob() to convert to and from base64 encoding.

There appears to be some confusion in the comments regarding what these functions accept/return, so…

• btoa() accepts a “string” where each character represents an 8-bit byte – if you pass a string containing characters that can’t be represented in 8 bits, it will probably break. This isn’t a problem if you’re actually treating the string as a byte array, but if you’re trying to do something else then you’ll have to encode it first.

• atob() returns a “string” where each character represents an 8-bit byte – that is, its value will be between 0 and 0xff. This does not mean it’s ASCII – presumably if you’re using this function at all, you expect to be working with binary data and not text.

See also:

• How do I load binary image data using Javascript and XMLHttpRequest?

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Most comments here are outdated. You can probably use both btoa() and atob(), unless you support really outdated browsers.

Check here:

• https://caniuse.com/?search=atob
• https://caniuse.com/?search=btoa