Basic info:

• Node.js version: 18.12.1
• jsdom version: 20.0.3

Minimal reproduction case

const { JSDOM } = require("jsdom")
const { document } = new JSDOM().window;

const div = document.createElement("div");
div.addEventListener("click", ({ offsetX, offsetY }) => console.log({ offsetX, offsetY }));
div.click();
// { offsetX: undefined, offsetY: undefined }

How does similar code behave in browsers?

const div = document.createElement("div");
div.addEventListener("click", ({ offsetX, offsetY }) => console.log({ offsetX, offsetY }));
div.click();
// { offsetX: 0, offsetY: 0 }

Details

The issue appears to be that jsdom doesn't support the CSSOM View extensions to MouseEvent (and possibly others). For parity with browsers and to make jsdom more useful, offsetX and offsetY attributes should be set and not return null/undefined. Since layout is out of scope for jsdom, 0 seems like the appropriate value to return (just as browsers do with synthetic click events).

Related Issues

• MouseEvent: x and y support #3470