noUnsafeReturn (JavaScript)

Language JavaScript (and super languages)

Summary

Rule available since: v2.6.3
Diagnostic Category: lint/nursery/noUnsafeReturn
This rule doesn’t have a fix.
The default severity of this rule is information.
This rule belongs to the following domains:
- types
Sources:
- Same as @typescript-eslint/no-unsafe-return

How to configure

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{
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  "linter": {
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    "rules": {
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      "nursery": {
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        "noUnsafeReturn": "error"
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      }
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    }
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  }
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}

Description

Disallow returning a value typed as any from a function.

TypeScript doesn’t check how values typed as any are used. When a function returns such a value, every caller receives it without type checking, which can hide bugs far away from where the any came from.

This rule reports functions that return a value typed as any or any[], and async functions that return a Promise<any>. It also reports returned values that use any in a type argument where the return type expects a specific type, such as returning a Set<any> from a function whose return type is Set<string>.

Returning any is allowed when the return type is declared as any or unknown, and returning any[] is allowed when the return type is unknown[].

Examples

Invalid

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function parse(text: string) {
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    return JSON.parse(text);
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}

/invalid-any.ts:2:5 lint/nursery/noUnsafeReturn ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This function returns a value of type any.
  
    1 │ function parse(text: string) {
  > 2 │     return JSON.parse(text);
      │     ^^^^^^^^^^^^^^^^^^^^^^^^
    3 │ }
    4 │ 
  
  ℹ TypeScript doesn't check values of type any, so callers can misuse the returned value without any error.
  
  ℹ Give the returned value a specific type. If the type isn't known in advance, use unknown instead, which requires callers to check the value before using it.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.

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const getItems = () => [] as any[];

/invalid-any-array.ts:1:24 lint/nursery/noUnsafeReturn ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This function returns a value of type any[].
  
  > 1 │ const getItems = () => [] as any[];
      │                        ^^^^^^^^^^^
    2 │ 
  
  ℹ TypeScript doesn't check values of type any, so callers can misuse the returned value without any error.
  
  ℹ Give the returned value a specific type. If the type isn't known in advance, use unknown instead, which requires callers to check the value before using it.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.

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declare const pending: Promise<any>;
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async function load() {
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    return pending;
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}

/invalid-promise-any.ts:3:5 lint/nursery/noUnsafeReturn ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This function returns a value of type Promise<any>.
  
    1 │ declare const pending: Promise<any>;
    2 │ async function load() {
  > 3 │     return pending;
      │     ^^^^^^^^^^^^^^^
    4 │ }
    5 │ 
  
  ℹ TypeScript doesn't check values of type any, so callers can misuse the returned value without any error.
  
  ℹ Give the returned value a specific type. If the type isn't known in advance, use unknown instead, which requires callers to check the value before using it.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.

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function getNames(): Set<string> {
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    return new Set<any>([1]);
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}

/invalid-type-argument.ts:2:5 lint/nursery/noUnsafeReturn ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This function returns a value that uses any where its return type expects a specific type.
  
    1 │ function getNames(): Set<string> {
  > 2 │     return new Set<any>([1]);
      │     ^^^^^^^^^^^^^^^^^^^^^^^^^
    3 │ }
    4 │ 
  
  ℹ TypeScript doesn't check values of type any, so callers can misuse the returned value without any error.
  
  ℹ Replace any in the type arguments of the returned value with the types that the return type expects.
  
  ℹ This rule belongs to the nursery group, which means it is not yet stable and may change in the future. Visit https://biomejs.dev/linter/#nursery for more information.

Valid

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function parse(text: string): unknown {
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    return JSON.parse(text);
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}
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function getNames(): Set<string> {
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    return new Set<string>(["a"]);
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}
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const getItems = () => ["a"];