Base64 javascript component

Base64.js

const chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
export default Base64 = {
    btoa: (input)  => {
        input = input || '';
        if(typeof input !== 'string'){
            throw new Error("Input must be string but you given "+(typeof input));
        }
        let str = input;
        let output = '';

        for (let block = 0, charCode, i = 0, map = chars;
             str.charAt(i | 0) || (map = '=', i % 1);
             output += map.charAt(63 & block >> 8 - i % 1 * 8)) {

            charCode = str.charCodeAt(i += 3/4);

            if (charCode > 0xFF) {
                throw new Error("'btoa' failed: The string to be encoded contains characters outside of the Latin1 range.");
            }

            block = block << 8 | charCode;
        }

        return output;
    },

    atob: (input) => {
        input = input || '';
        if(typeof input !== 'string'){
            throw new Error("Input must be string but you given "+(typeof input));
        }
        let str = input.replace(/=+$/, '');
        let output = '';

        if (str.length % 4 == 1) {
            throw new Error("'atob' failed: The string to be decoded is not correctly encoded.");
        }
        for (let bc = 0, bs = 0, buffer, i = 0;
             buffer = str.charAt(i++);

             ~buffer && (bs = bc % 4 ? bs * 64 + buffer : buffer,
             bc++ % 4) ? output += String.fromCharCode(255 & bs >> (-2 * bc & 6)) : 0
        ) {
            buffer = chars.indexOf(buffer);
        }

        return output;
    }
};