I'm confused by your advice, honestly. Defold is definitely not ultra-light, it's a whole ide/studio engine. If I was recommending for ease of entry, I'd 100% pick a "fantasy console" like Pico-8[1] or one of the many alternatives[2] that are free and use a different language if Lua isn't the person's thing.

Second, Phaser[3] actually IS regular javascript. It's the opposite of Defold that is a whole node based editor thing. Phaser is just a an API you use in a script file, that you just splonk into your html page. I don't know how much more standard JS you can get than that.

[1]: https://www.lexaloffle.com/pico-8.php

[2]: https://github.com/paladin-t/fantasy

[3]: https://docs.phaser.io/phaser/getting-started/set-up-dev-env... (linked to the hello world example)