Simple explanation, examples in an an editor that can be played with and executed, argument names and explanations, browser compatibility, etc etc etc
Compared to the amount of languages where their documentation is a table auto-generated from code, it's everything I could dream of!
w3schools style "Let me walk you through every step of the process" probably.
It has it's place, I know I've found it useful in the past, but definitely not a place you want to stay in very long.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...
https://www.w3schools.com/jsref/jsref_pow.asp
W3 doesn't have much in terms of English explanation, has less examples, and their playground forwards you to another page as opposed to MDN where it's embedded.
The funny thing is, I don't know that the resulting product is really much better.
MDN is richer, more exact, more complete. But being minimal is better when you already unfamiliar with basics.
TLDR : MDN pair well with W3School, imo both are fine as they are.