It's almost too simple for a standalone example. First follow the getting Electron Quick Start guide (
https://www.electronjs.org/docs/latest/tutorial/quick-start) until you get to the point where an "npm start" gives you an Electron window with the "Hello World" message.
Next you need the three output files (.html, .js, wasm) from an Emscripten build, let's call them c64.html, c64.wasm and c64.js - you can download examples from here:
Put those files into the project root directory where the index.html file is.
Next, in the main.js file, where the index.html is loaded, replace index.html with c64.html:
win.loadFile('c64.html');
Next, run 'npm start'. Voilà, C64 emulator in Electron ;)