Avoid extra non-null assertions

Docs > Code Analysis > Static Analysis Rules > Avoid extra non-null assertions

This page is not yet available in Spanish. We are working on its translation.
If you have any questions or feedback about our current translation project, feel free to reach out to us!

Metadata

ID: typescript-best-practices/no-extra-non-null-assertion

Language: TypeScript

Severity: Error

Category: Error Prone

Description

The non null or undefined assertion operation should not be used twice in a single expression.

Non-Compliant Code Examples

const bar = foo!!.bar;
function foo(bar: number | undefined) { const bar: number = bar!!; }
function foo(bar?: { n: number }) { return bar!?.n; }
function foo(bar?: { n: number }) { return bar!?.(); }

// parentheses
const foo: { bar: number } | null = null; const bar = (foo!)!.bar;
function foo(bar?: { n: number }) { return (bar!)?.n; }
function foo(bar?: { n: number }) { return (bar)!?.n; }
function foo(bar?: { n: number }) { return (bar!)?.(); }

Compliant Code Examples

const bar = foo!.bar;

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

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

// https://github.com/typescript-eslint/typescript-eslint/issues/2166
checksCounter?.textContent!.trim();

// https://github.com/typescript-eslint/typescript-eslint/issues/2732
function foo(key: string | null) {
  const obj = {};
  return obj?.[key!];
}