Avoid the any type

Docs > Code Analysis > Static Analysis Rules > Avoid the any type

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Metadata

ID: typescript-best-practices/no-explicit-any

Language: TypeScript

Severity: Notice

Category: Best Practices

Description

Do not use the any type, as it is too broad and can lead to unexpected behavior.

Non-Compliant Code Examples

const number: any = 1
function generic(): any {}
function generic(): Array<any> {}
function generic(): any[] {}
function generic(param: Array<any>): number {}
function generic(param: any[]): number {}
function generic(param: Array<any>): Array<any> {}

function generic(): Array<Array<any>> {}
function generic(): Array<any[]> {}

class Greeter { constructor(param: Array<any>) {} }
class Greeter { message: any; }

class Greeter { message: Array<any>; }
class Greeter { message: any[]; }
class Greeter { message: Array<Array<any>>; }
class Greeter { message: Array<any[]>; }

interface Greeter { message: any; }
interface Greeter { message: Array<any>; }
interface Greeter { message: any[]; }
interface Greeter { message: Array<Array<any>>; }
interface Greeter { message: Array<any[]>; }
type obj = { message: any; }
type obj = { message: Array<any>; }
type obj = { message: any[]; }
type obj = { message: Array<Array<any>>; }
type obj = { message: Array<any[]>; }
type obj = { message: string | any; }
type obj = { message: string | Array<any>; }
type obj = { message: string | any[]; }
type obj = { message: string | Array<Array<any>>; }
type obj = { message: string | Array<any[]>; }
type obj = { message: string & any; }
type obj = { message: string & Array<any>; }
type obj = { message: string & any[]; }
type obj = { message: string & Array<Array<any>>; }
type obj = { message: string & Array<any[]>; }
class Foo<t = any> extends Bar<any> {}
abstract class Foo<t = any> extends Bar<any> {}
abstract class Foo<t = any> implements Bar<any>, Baz<any> {}
new Foo<any>()
Foo<any>()

// https://github.com/typescript-eslint/typescript-eslint/issues/64
function test<T extends Partial<any>>() {}
const test = <T extends Partial<any>>() => {};
function foo(a: number, ...rest: any[]): void { return; }
type Any = any;
function foo5(...args: any) {}

const bar5 = function (...args: any) {}
const baz5 = (...args: any) => {}
interface Qux5 { (...args: any): void; }
function quux5(fn: (...args: any) => void): void {}
function quuz5(): ((...args: any) => void) {}
type Fred5 = (...args: any) => void;
type Corge5 = new (...args: any) => void;
interface Grault5 { new (...args: any): void; }
interface Garply5 { f(...args: any): void; }
declare function waldo5(...args: any): void;

Compliant Code Examples

const number: number = 1;
function greet(): string {}
function greet(): Array<string> {}
function greet(): string[] {}
function greet(): Array<Array<string>> {}
function greet(): Array<string[]> {}
function greet(param: Array<string>): Array<string> {}

class Greeter { message: string; }
class Greeter { message: Array<string>; }
class Greeter { message: string[]; }
class Greeter { message: Array<Array<string>>; }
class Greeter { message: Array<string[]>; }
interface Greeter { message: string; }
interface Greeter { message: Array<string>; }
interface Greeter { message: string[]; }
interface Greeter { message: Array<Array<string>>; }
interface Greeter { message: Array<string[]>; }
type obj = { message: string; };
type obj = { message: Array<string>; };
type obj = { message: string[]; };
type obj = { message: Array<Array<string>>; };
type obj = { message: Array<string[]>; };
type obj = { message: string | number };
type obj = { message: string | Array<string>; };
type obj = { message: string | string[]; };
type obj = { message: string | Array<Array<string>>; };
type obj = { message: string & number; };
type obj = { message: string & Array<string>; };
type obj = { message: string & string[]; };
type obj = { message: string & Array<Array<string>>; };

// rest params enforces due to no options
// https://github.com/eslint/typescript-eslint-parser/issues/397
// function foo(a: number, ...rest: any[]): void { return; }
// function foo1(...args: any[]) {}
// const bar1 = function (...args: any[]) {};
// const baz1 = (...args: any[]) => {};
// function foo2(...args: readonly any[]) {}
// const bar2 = function (...args: readonly any[]) {};
// const baz2 = (...args: readonly any[]) => {};
// function foo3(...args: Array<any>) {}
// const bar3 = function (...args: Array<any>) {};
// const baz3 = (...args: Array<any>) => {};
// function foo4(...args: ReadonlyArray<any>) {}
// const bar4 = function (...args: ReadonlyArray<any>) {};
// const baz4 = (...args: ReadonlyArray<any>) => {};

// interface Qux1 { (...args: any[]): void; }
// interface Qux2 { (...args: readonly any[]): void; }
// interface Qux3 { (...args: Array<any>): void; }
// interface Qux4 { (...args: ReadonlyArray<any>): void; }

// function quux1(fn: (...args: any[]) => void): void {}
// function quux2(fn: (...args: readonly any[]) => void): void {}
// function quux3(fn: (...args: Array<any>) => void): void {}
// function quux4(fn: (...args: ReadonlyArray<any>) => void): void {}
// function quuz1(): (...args: any[]) => void {}
// function quuz2(): (...args: readonly any[]) => void {}
// function quuz3(): (...args: Array<any>) => void {}
// function quuz4(): (...args: ReadonlyArray<any>) => void {}
// type Fred1 = (...args: any[]) => void;
// type Fred2 = (...args: readonly any[]) => void;
// type Fred3 = (...args: Array<any>) => void;
// type Fred4 = (...args: ReadonlyArray<any>) => void;
// type Corge1 = new (...args: any[]) => void;
// type Corge2 = new (...args: readonly any[]) => void;
// type Corge3 = new (...args: Array<any>) => void;
// type Corge4 = new (...args: ReadonlyArray<any>) => void;

// interface Grault1 { new (...args: any[]): void; }
// interface Grault2 { new (...args: readonly any[]): void; }
// interface Grault3 { new (...args: Array<any>): void; }
// interface Grault4 { new (...args: ReadonlyArray<any>): void; }
// interface Garply1 { f(...args: any[]): void; }
// interface Garply2 { f(...args: readonly any[]): void; }
// interface Garply3 { f(...args: Array<any>): void; }
// interface Garply4 { f(...args: ReadonlyArray<any>): void; }

// declare function waldo1(...args: any[]): void;
// declare function waldo2(...args: readonly any[]): void;
// declare function waldo3(...args: Array<any>): void;
// declare function waldo4(...args: ReadonlyArray<any>): void;