How to put a dot in a function (ex.: lib.genarate() )

Question

How can I put a dot in a function in javascript? I have searched, but nothing!
For example:
lib.execute(); or hi.start();

I tried:

function go.abc() {
  document.write('Hello world');
}

<button onclick="go.abc();">Click me</button>

And I receive this:

 Error: {
  "message": "Uncaught ReferenceError: go is not defined",
  "filename": "https://stacksnippets.net/js",
  "lineno": 12,
  "colno": 29
}

I have seen somewhere that it used variables, but it was not docs and I do not remember how to use it