JavaScript Base64函數

function base64_encode (data) {  // http://kevin.vanzonneveld.net  // +   original by: Tyler Akins (http://rumkin.com)  // +   improved by: Bayron Guevara  // +   improved by: Thunder.m  // +   improved by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)  // +   bugfixed by: Pellentesque Malesuada  // +   improved by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)  // +   improved by: Rafa? Kukawski (http://kukawski.pl)  // *     example 1: base64_encode('Kevin van Zonneveld');  // *     returns 1: 'S2V2aW4gdmFuIFpvbm5ldmVsZA=='  // mozilla has this native  // - but breaks in 2.0.0.12!  //if (typeof this.window['btoa'] == 'function') {  //    return btoa(data);  //}  var b64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";  var o1, o2, o3, h1, h2, h3, h4, bits, i = 0,    ac = 0,    enc = "",    tmp_arr = [];  if (!data) {    return data;  }  do { // pack three octets into four hexets    o1 = data.charCodeAt(i++);    o2 = data.charCodeAt(i++);    o3 = data.charCodeAt(i++);    bits = o1 << 16 | o2 << 8 | o3;    h1 = bits >> 18 & 0x3f;    h2 = bits >> 12 & 0x3f;    h3 = bits >> 6 & 0x3f;    h4 = bits & 0x3f;    // use hexets to index into b64, and append result to encoded string    tmp_arr[ac++] = b64.charAt(h1) + b64.charAt(h2) + b64.charAt(h3) + b64.charAt(h4);  } while (i < data.length);  enc = tmp_arr.join('');  var r = data.length % 3;  return (r ? enc.slice(0, r - 3) : enc) + '==='.slice(r || 3);}