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no-non-null-assertion

Disallow non-null assertions using the ! postfix operator.

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Extending "plugin:@typescript-eslint/strict" in an ESLint configuration enables this rule.

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Some problems reported by this rule are manually fixable by editor suggestions.

TypeScript's ! non-null assertion operator asserts to the type system that an expression is non-nullable, as in not null or undefined. Using assertions to tell the type system new information is often a sign that code is not fully type-safe. It's generally better to structure program logic so that TypeScript understands when values may be nullable.

.eslintrc.cjs
module.exports = {
  "rules": {
    "@typescript-eslint/no-non-null-assertion": "error"
  }
};
Try this rule in the playground ↗

Examples​

interface Example {
  property?: string;
}

declare const example: Example;
const includesBaz = example.property!.includes('baz');

Options​

This rule is not configurable.

When Not To Use It​

If your project does not use the strictNullChecks compiler option, this rule is likely useless to you. If your code is often wildly incorrect with respect to strict null-checking, your code may not yet be ready for this rule.

Resources​