typescript/no-extra-non-null-assertion Correctness

✅ This rule is turned on by default.

What it does

Disallow extra non-null assertions.

Why is this bad?

The ! non-null assertion operator in TypeScript is used to assert that a value's type does not include null or undefined. Using the operator any more than once on a single value does nothing.

Examples

Examples of incorrect code for this rule:

const foo: { bar: number } | null = null;
const bar = foo!!!.bar;

function foo(bar: number | undefined) {
  const bar: number = bar!!!;
}

function foo(bar?: { n: number }) {
  return bar!?.n;
}

Examples of correct code for this rule:

const foo: { bar: number } | null = null;
const bar = foo!.bar;

function foo(bar: number | undefined) {
  const bar: number = bar!;
}

function foo(bar?: { n: number }) {
  return bar?.n;
}

How to use

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

CLI

oxlint --deny typescript/no-extra-non-null-assertion

Config (.oxlintrc.json)

{
  "rules": {
    "typescript/no-extra-non-null-assertion": "error"
  }
}

References

• Rule Source