@putout/plugin-typescript

@putout/plugin-typescript

TypeScript is JavaScript with syntax for types.

(c) typescriptcriptlang.org

🐊Putout plugin adds ability to transform TypeScript code. Enabled by default for ts and tsx files.

Install

npm i putout @putout/plugin-typescript -D

Options

{
    "rules": {
        "typescript/apply-as-type-assertion": "on",
        "typescript/apply-utility-types": "on",
        "typescript/apply-type-guards": "on",
        "typescript/convert-generic-to-shorthand": "on",
        "typescript/remove-duplicates-from-union": "on",
        "typescript/remove-duplicates-interface-keys": "on",
        "typescript/remove-duplicates-exports": "on",
        "typescript/remove-useless-types-from-constants": "on",
        "typescript/remove-unused-types": "on",
        "typescript/remove-useless-types": "on",
        "typescript/remove-useless-parens": "on",
        "typescript/remove-useless-mapped-types": "on"
    }
}

Rules

apply-as-type-assertion

According to best practise.

❌ Example of incorrect code

const boundaryElement = <HTMLElement>e.target;

✅ Example of correct code

const boundaryElement1 = e.target as HTMLElement;

apply-utility-types

❌ Example of incorrect code

type SuperType1 = {
    [Key in keyof Type]?: Type[Key];
};

✅ Example of correct code

type SuperType1 = Partial<Type>;

apply-type-guards

It just so happens that TypeScript has something called a type guard. A type guard is some expression that performs a runtime check that guarantees the type in some scope.

(c) typescript.org

Check out in 🐊Putout Editor.

❌ Example of incorrect code

const isNumber = (a) => typeof a === 'number';

✅ Example of correct code

const isNumber = (a): a is number => typeof a === 'number';

convert-generic-to-shorthand

There is no difference at all. Type[] is the shorthand syntax for an array of Type. Array<Type> is the generic syntax. They are completely equivalent.

(c) https://stackoverflow.com/a/36843084/4536327

Convert generic to shorthand.

❌ Example of incorrect code

interface A {
    x: Array<X>;
    y: Array<X | Y>;
}

✅ Example of correct code

interface A {
    x: X[];
    y: X[] | Y[];
}

Comparison

Linter	Rule	Fix
🐊 Putout	typescript/convert-generic-to-shorthand	✅
⏣ ESLint	@typescript-eslint/array-type	✅

remove-duplicates-from-union

❌ Example of incorrect code

type x = boolean[]
    | A
    | string
    | A
    | string[]
    | boolean[];

✅ Example of correct code

type x = boolean[]
    | A
    | string
    | string[];

remove-duplicates-exports

In JavaScript duplicate exports leads to SyntaxError, anyways TypeScript parses such code and reports Duplicates Identifier diagnostic.

It gives us ability to automate fixing of such code 😏. Check it out in 🐊Putout Editor.

❌ Example of incorrect code

export {
    a,
    hello,
    a,
    world,
};

✅ Example of correct code

export {
    hello,
    a,
    world,
};

☝️ The rule fits good with putout/add-newlines-between-specifiers of eslint-plugin-putout.

remove-useless-types-from-constants

❌ Example of incorrect code

const x: any = 5;

✅ Example of correct code

const x = 5;

remove-unused-types

❌ Example of incorrect code

type n = number;
type s = string;

const x: n = 5;

✅ Example of correct code

type n = number;

const x: n = 5;

remove-useless-types

❌ Example of incorrect code

type oldType = {
    a: number;
    b: string;
};
type newType = oldType;

const x: newType = {
    a: 5,
    b: 'hello',
};

✅ Example of correct code

type oldType = {
    a: number;
    b: string;
};

const x: oldType = {
    a: 5,
    b: 'hello',
};

remove-useless-parens

Check it out in 🐊Putout Editor.

❌ Example of incorrect code

const x: (X | Y)[] = [];
const m: (X)[] = [];
const z: (X | Y) = 5;
const f: (X) = 5;

✅ Example of correct code

const x: X[] | Y[] = [];
const m: X[] = [];
const z: X | Y = 5;
const f: X = 5;

remove-useless-mapped-types

Remove useless mapped types.

❌ Example of incorrect code

type SuperType = {
    [Key in keyof Type]: Type[Key];
};

✅ Example of correct code

type SuperType = Type;

remove-useless-mapping-modifiers

Remove useless mapping modifiers.

❌ Example of incorrect code

type SuperType = {
    [Key in keyof Type]+?: Type[Key];
};

✅ Example of correct code

type SuperType = {
    [Key in keyof Type]?: Type[Key];
};

remove-duplicate-interface-keys

❌ Example of incorrect code

interface Hello {
    'hello': any;
    'hello': string;
}

✅ Example of correct code

interface Hello {
    'hello': string;
}

License

MIT