description |
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Disallow returning a value with type `any` from a function. |
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🛑 This file is source code, not the primary documentation location! 🛑
See https://typescript-eslint.io/rules/no-unsafe-return for documentation.
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>
.
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]);
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[];
}
If your codebase has many existing any
s 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.