When I was using typescript this still came up if you missed an array bounds check, you'd end up with an unexpected undefined. Pretty annoying and tough to debug.
Has this changed (I can't see how it could have, but... maybe?)
var foos1 = [] as Foo[],
foos2 = [] as (Foo | undefined)[];
// ... later
var foo1 = foos1[i],
foo2 = foos2[i];
foo1.bar(); // types fine, TS assumes non-undefined
foo2.bar(); // TS type error, as you haven't checked undef
if (foo2) foo2.bar(); // types fine, undef excludedE.g. if I missed a bounds check, and access past the end of a `Foo[]`, it would be typed as `Foo` (and not `Foo | undefined`), but really be `undefined.
Consider this code.
var foos: Foo[] = [new Foo()];
foos[1].bar();
Obviously it's bad if I forget a bounds check, but it's similarly bad if I forgot a null check.
Of course, I understand why this issue exists, but it is an issue.
This says "either an array of Foo or an array of undefined", right? Not "either an array of Foo or just undefined"?
Foo[] | undefined[] means either 1) an array of Foo, or 2) an array of undefined.