Avoid extra non-null assertions

Docs > コード分析 > Static Analysis Rules > Avoid extra non-null assertions

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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!];
}