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no-unsafe-return

Disallow returning a value with type any from a function.

✅

Extending "plugin:@typescript-eslint/recommended-type-checked" in an ESLint configuration enables this rule.

💭

This rule requires type information to run.

The any type in TypeScript is a dangerous "escape hatch" from the type system. Using any disables many type checking rules and is generally best used only as a last resort or when prototyping code.

Despite your best intentions, the any type can sometimes leak into your codebase. Returning an an any-typed value from a function creates a potential type safety hole and source of bugs in your codebase.

This rule disallows returning any or any[] from a function.

This rule also compares generic type argument types to ensure you don't return an unsafe any in a generic position to a function that's expecting a specific type. For example, it will error if you return Set<any> from a function declared as returning Set<string>.

.eslintrc.cjs
module.exports = {
  "rules": {
    "@typescript-eslint/no-unsafe-return": "error"
  }
};

Try this rule in the playground ↗

Examples​

function foo1() {
  return 1 as any;
}
function foo2() {
  return Object.create(null);
}
const foo3 = () => {
  return 1 as any;
};
const foo4 = () => Object.create(null);

function foo5() {
  return [] as any[];
}
function foo6() {
  return [] as Array<any>;
}
function foo7() {
  return [] as readonly any[];
}
function foo8() {
  return [] as Readonly<any[]>;
}
const foo9 = () => {
  return [] as any[];
};
const foo10 = () => [] as any[];

const foo11 = (): string[] => [1, 2, 3] as any[];

// generic position examples
function assignability1(): Set<string> {
  return new Set<any>([1]);
}
type TAssign = () => Set<string>;
const assignability2: TAssign = () => new Set<any>([true]);
Open in Playground

There are cases where the rule allows to return any to unknown.

Examples of any to unknown return that are allowed:

function foo1(): unknown {
  return JSON.parse(singleObjString); // Return type for JSON.parse is any.
}

function foo2(): unknown[] {
  return [] as any[];
}
Open in Playground

Options​

This rule is not configurable.

When Not To Use It​

If your codebase has many existing anys or areas of unsafe code, it may be difficult to enable this rule. It may be easier to skip the no-unsafe-* rules pending increasing type safety in unsafe areas of your project. You might consider using ESLint disable comments for those specific situations instead of completely disabling this rule.

Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting. See Troubleshooting > Linting with Type Information > Performance if you experience performance degredations after enabling type checked rules.

Resources​