no-non-null-asserted-optional-chain.md
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no-non-null-asserted-optional-chain
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Disallows using a non-null assertion after an optional chain expression (Rule Details
Optional chain expressions are designed to return undefined
if the optional property is nullish.
Using non-null assertions after an optional chain expression is wrong, and introduces a serious type safety hole into your code.
Examples of incorrect code for this rule:
/* eslint @typescript-eslint/no-non-null-asserted-optional-chain: "error" */
foo?.bar!;
foo?.bar()!;
// Prior to TS3.9, foo?.bar!.baz meant (foo?.bar).baz - i.e. the non-null assertion is applied to the entire chain so far.
// For TS3.9 and greater, the non-null assertion is only applied to the property itself, so it's safe.
// The following is incorrect code if you're using less than TS3.9
foo?.bar!.baz;
foo?.bar!();
foo?.bar!().baz;
Examples of correct code for this rule:
/* eslint @typescript-eslint/no-non-null-asserted-optional-chain: "error" */
foo?.bar;
(foo?.bar).baz;
foo?.bar();
foo?.bar();
foo?.bar().baz;
// The following is correct code if you're using TS3.9 or greater
foo?.bar!.baz;
foo?.bar!();
foo?.bar!().baz;
When Not To Use It
If you are not using TypeScript 3.7 (or greater), then you will not need to use this rule, as the operator is not supported.