no-explicit-any.md

Pattern: Explicit any type usage

Issue: -

Description

The any type disables TypeScript's type checking and should be avoided. Using any undermines the purpose of TypeScript's type system and can hide real type errors. Instead, use specific types or unknown when the type cannot be known in advance.

Examples

Example of incorrect code:

// any as variable type
let value: any;

// any in arrays
const items: any[] = [];
const list: Array<any> = [];

// any in function parameters
function process(data: any) {}

// any in function return
function getData(): any {}

// any in generic types
type Container<T = any> = { data: T };

// any in type assertions
const result = data as any;

// Nested any in arrays
const matrix: any[][] = [];

Example of correct code:

// Specific types
let value: string;
let mixed: string | number;

// Typed arrays
const items: string[] = [];
const list: Array<number> = [];

// Unknown for uncertain types
function process(data: unknown) {}

// Union types for multiple possibilities
type Status = 'pending' | 'success' | 'error';

// Proper generic constraints
type Container<T extends object> = { data: T };

// Type assertions to known types
const result = data as string;

// Type-safe array definitions
const matrix: number[][] = [];

// Rest parameters with specific types
function log(...messages: string[]) {}