typescript/no-non-null-asserted-nullish-coalescing Restriction

What it does

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

Why is this bad?

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

Examples of incorrect code for this rule:

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

let x!: string;
x! ?? "";

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

Examples of correct code for this rule:

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! ?? "";

How to use

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

CLI

oxlint --deny typescript/no-non-null-asserted-nullish-coalescing

Config (.oxlintrc.json)

{
  "rules": {
    "typescript/no-non-null-asserted-nullish-coalescing": "error"
  }
}

References

• Rule Source