typescript/no-non-null-asserted-optional-chain Correctness

✅ This rule is turned on by default.

🛠️ An auto-fix is available for this rule.

What it does

Disallow non-null assertions after an optional chain expression.

Why is this bad?

By design, optional chain expressions (?.) provide undefined as the expression's value, if the object being accessed is null or undefined, instead of throwing an error. Using a non-null assertion (!) to assert the result of an optional chain expression is contradictory and likely wrong, as it indicates the code is both expecting the value to be potentially null or undefined and non-null at the same time.

In most cases, either:

1. The object is not nullable and did not need the ?. for its property lookup
2. The non-null assertion is incorrect and introduces a type safety hole.

Examples

Examples of incorrect code for this rule:

foo?.bar!;
foo?.bar()!;

Examples of correct code for this rule:

foo?.bar;
foo.bar!;

How to use

To enable this rule in the CLI or using the config file, you can use:

CLI

oxlint --deny typescript/no-non-null-asserted-optional-chain

Config (.oxlintrc.json)

{
  "rules": {
    "typescript/no-non-null-asserted-optional-chain": "error"
  }
}

References

• Rule Source