why browser is throwing error for base64url encoded code example

Example: base64 to string and string to base64 javascript decode

// base64 to string
let base64ToString = Buffer.from(obj, "base64").toString();
base64ToString = JSON.parse(base64ToString);

//or
let str = 'bmltZXNoZGV1amEuY29t';
let buff = new Buffer(str, 'base64');
let base64ToStringNew = buff.toString('ascii');

// string to base64
let data = 'nimeshdeuja.com';
let buff = new Buffer(data);
let stringToBase64 = buff.toString('base64');