Non-null assertions infringe a responsibility of optional chaining

Because @RyanCavanaugh couldn't understand what is the problem, I reexplain it.

In the following case, a responsibility of optional chaining is making a return type Element | undefined.

// a is string | null | undefined
const a = document.querySelector('_')?.textContent;

In the following case, non-null assertion has broken the safeness made by optional chaining.

// a is string
const a = document.querySelector('_')?.textContent!;

It is obvious that optional chaining was not considered when non-null assertion operator was designed. TypeScript has to consider what is the best design and what to do via reconsidering the design of non-null assertion operator.

TypeScript Version: 3.7.x-dev.20191105

Search Terms:

Code

const a = document.querySelector('_')?.textContent!;

Expected behavior:

a is string | undefined.

Actual behavior:

a is string.

Playground Link:

Related Issues:

No file or test is named. Start by reproducing the reported TypeScript type-checking example with optional chaining followed by a non-null assertion, then trace how these operators determine the inferred type. Done means the behavior is resolved according to the expected type and covered by a regression test.