JS.TS.NO.NON.NULL.ASSERTED.NULLISH.COALESCING
Disallow non-null assertions in the left operand of a nullish coalescing operator
Rule Details
The nullish coalescing operator is designed to provide a default value when dealing with null or undefined.
Using non-null assertions in the left operand of the nullish coalescing operator is redundant.
Examples of code for this rule:
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Incorrect
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/* eslint @typescript-eslint/no-non-null-asserted-nullish-coalescing: "error" */
foo! ?? bar;
foo.bazz! ?? bar;
foo!.bazz! ?? bar;
foo()! ?? bar;
let x!: string;
x! ?? '';
let x: string;
x = foo();
x! ?? '';
Correct
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/* eslint @typescript-eslint/no-non-null-asserted-nullish-coalescing: "error" */
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! ?? '';
Options
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// .eslintrc.json
{
"rules": {
"@typescript-eslint/no-non-null-asserted-nullish-coalescing": "warn"
}
}
This rule is not configurable.
When Not To Use It
If you are not using TypeScript 3.7 (or greater), then you will not need to use this rule, as the nullish coalescing operator is not supported.
Further Reading
- TypeScript 3.7 Release Notes (https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-7.html)
- Nullish Coalescing Proposal (https://github.com/tc39/proposal-nullish-coalescing)