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no-unsafe-assignment

Disallow assigning a value with type any to variables and properties.

✅

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. Assigning an any typed value to a variable can be hard to pick up on, particularly if it leaks in from an external library.

This rule disallows assigning any to a variable, and assigning any[] to an array destructuring.

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

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

Try this rule in the playground ↗

Examples​

const x = 1 as any,
  y = 1 as any;
const [x] = 1 as any;
const [x] = [] as any[];
const [x] = [1 as any];
[x] = [1] as [any];

function foo(a = 1 as any) {}
class Foo {
  constructor(private a = 1 as any) {}
}
class Foo {
  private a = 1 as any;
}

// generic position examples
const x: Set<string> = new Set<any>();
const x: Map<string, string> = new Map<string, any>();
const x: Set<string[]> = new Set<any[]>();
const x: Set<Set<Set<string>>> = new Set<Set<Set<any>>>();
Open in Playground

There are cases where the rule allows assignment of any to unknown.

Example of any to unknown assignment that are allowed:

const x: unknown = y as any;
const x: unknown[] = y as any[];
const x: Set<unknown> = y as Set<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​