The subscribe() method can accept callback function definitions in line, for next, error, and complete handlers. It is known as shorthand notation or Subscribe method with positional arguments.
For example, you can define subscribe method as below,
myObservable.subscribe(
x => console.log('Observer got a next value: ' + x),
err => console.error('Observer got an error: ' + err),
() => console.log('Observer got a complete notification')
);