polyfill-service/polyfills/atob/polyfill.js

A polyfill combinator

(function (global) {
	var keys = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=', keysRe = new RegExp('[^' + keys + ']');

	// <Global>.atob
	global.atob = function atob(input) {
		var output = [], buffer, bufferB, chrs, index = 0, indexB, length = input.length;

		if ((keysRe.test(input)) || (/=/.test(input) && (/=[^=]/.test(input) || /={3}/.test(input)))) {
			throw new Error('Invalid base64 data');
		}

		if (length % 4 > 0) {
			input += Array(4 - length % 4 + 1).join("=");
			length = input.length;
		}

		while (index < length) {
			for (bufferB = [], indexB = index; index < indexB + 4;) {
				bufferB.push(keys.indexOf(input.charAt(index++)));
			}

			buffer = (bufferB[0] << 18) + (bufferB[1] << 12) + ((bufferB[2] & 63) << 6) + (bufferB[3] & 63);

			chrs = [(buffer & (255 << 16)) >> 16, bufferB[2] === 64 ? -1 : (buffer & (255 << 8)) >> 8, bufferB[3] === 64 ? -1 : buffer & 255];

			for (indexB = 0; indexB < 3; ++indexB) {
				if (chrs[indexB] >= 0 || indexB === 0) {
					output.push(String.fromCharCode(chrs[indexB]));
				}
			}
		}

		return output.join('');
	};

	// <Global>.btoa
	global.btoa = function btoa(input) {
		var output = [], buffer, chrs, index = 0, length = input.length;

		while (index < length) {
			chrs = [input.charCodeAt(index++), input.charCodeAt(index++), input.charCodeAt(index++)];

			buffer = (chrs[0] << 16) + ((chrs[1] || 0) << 8) + (chrs[2] || 0);

			output.push(
				keys.charAt((buffer & (63 << 18)) >> 18),
				keys.charAt((buffer & (63 << 12)) >> 12),
				keys.charAt(isNaN(chrs[1]) ? 64 : (buffer & (63 << 6)) >> 6),
				keys.charAt(isNaN(chrs[2]) ? 64 : (buffer & 63))
			);
		}

		return output.join('');
	};
})(this);