Right-click anywhere in the webpage and then select Inspect. Or, press F12. DevTools opens next to the webpage.
Error messages appear in the Console:
The demo page uses the following code:
function first(name) { second(name); } function second(name) { third(name); } function third(name) { if (!name) { console.error(`Name isn't defined :(`) } else { console.assert( name.length