no-non-null-asserted-nullish-coalescing.mdx

description
Disallow non-null assertions in the left operand of a nullish coalescing operator.

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See https://typescript-eslint.io/rules/no-non-null-asserted-nullish-coalescing for documentation.

The ?? nullish coalescing runtime operator allows providing a default value when dealing with null or undefined. Using a ! non-null assertion type operator in the left operand of a nullish coalescing operator is redundant, and likely a sign of programmer error or confusion over the two operators.

Examples

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

let x!: string;
x! ?? '';

let x: string;
x = foo();
x! ?? '';

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

// This is considered correct code because there's no way for the user to satisfy it.
let x: string;
x! ?? '';

When Not To Use It

If your project's types don't yet fully describe whether certain values may be nullable, such as if you're transitioning to strictNullChecks, this rule might create many false reports. You might consider using ESLint disable comments for those specific situations instead of completely disabling this rule.

Further Reading

• TypeScript 3.7 Release Notes
• Nullish Coalescing Proposal