matchAll Throws error when g flag is missing now?
The information presented to you on MDN, in this instance, is wrong.
The Official ECMA Specification, ECMA-262 as of February 15, 2020( See here ), states that if there is no g flag present, that matchAll should throw a TypeError.
See specifically 2.b.iii below.
The error message is obviously fairly confusing with its phrasing, but still correct.