no-unsafe-return.md

no-unsafe-return

Disallows returning any from a function.

Despite your best intentions, the any type can sometimes leak into your codebase. Returned any typed values are not checked at all by TypeScript, so it creates a potential safety hole, and source of bugs in your codebase.

Rule Details

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

Examples of code for this rule:

❌ Incorrect

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]);

✅ Correct

function foo1() {
  return 1;
}
function foo2() {
  return Object.create(null) as Record<string, unknown>;
}

const foo3 = () => [];
const foo4 = () => ['a'];

function assignability1(): Set<string> {
  return new Set<string>(['foo']);
}
type TAssign = () => Set<string>;
const assignability2: TAssign = () => new Set(['foo']);

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[];
}

Options

// .eslintrc.json
{
  "rules": {
    "@typescript-eslint/no-unsafe-return": "error"
  }
}

This rule is not configurable.

Related To

• no-explicit-any
• TSLint: no-unsafe-any

Attributes

• Configs:
  • ✅ Recommended
  • 🔒 Strict
• 🔧 Fixable
• 💭 Requires type information