Ketik inferensi dengan TypeScript menggunakan konstruk sebagai const dan kata kunci inferior

Ketik Dasar-dasar Inferensi

let variable;

let variable = 'Hello!';

function getRandomInteger(max: number) {
  return Math.floor(Math.random() * max);
}

Ketik inferensi dalam obat generik

function getProperty<ObjectType, KeyType extends keyof ObjectType>(
  object: ObjectType, key: KeyType
) {
  return object[key];
}

const dog = {
  name: 'Fluffy'
};
getProperty(dog, 'name');

Menggunakan kata kunci yang disimpulkan

function call<ReturnType>(
  functionToCall: (...args: any[]) => ReturnType, ...args: any[]
): ReturnType {
  return functionToCall(...args);
}

const randomNumber = call(getRandomInteger, 100);

const randomNumber = call(getRandomInteger, '100'); //   

function call<ArgumentsType extends any[], ReturnType>(
  functionToCall: (...args: ArgumentsType) => ReturnType, ...args: ArgumentsType
): ReturnType {
  return functionToCall(...args);
}

const randomNumber = call(getRandomInteger, '100');

Argument of type ‘”100″‘ is not assignable to parameter of type ‘number’.

type Option = [string, boolean];
const option: Option = ['lowercase', true];

Fitur Kata Kunci disimpulkan

type FunctionReturnType<FunctionType extends (...args: any) => ?> = ?;

type FunctionReturnType<ReturnType, FunctionType extends (...args: any) => ReturnType> = ReturnType;
FunctionReturnType<number, typeof getRandomInteger>;

type FunctionReturnType<FunctionType extends (args: any) => any> = FunctionType extends (...args: any) => infer ReturnType ? ReturnType : any;

• Dikatakan FunctionTypeberkembang di sini (args: any) => any.
• Kami menunjukkan bahwa FunctionReturnTypeini adalah tipe bersyarat.
• Kami memeriksa apakah itu mengembang FunctionType (...args: any) => infer ReturnType.

FunctionReturnType<typeof getRandomInteger>; // number

Bangun sebagai const

let fruit = 'Banana';
const carrot = 'Carrot';

let fruit = 'Banana' as const;

const user = {
  name: 'John',
  role: 'admin'
};

const user: {
  name: string,
  role: string
};

const user = {
  name: 'John',
  role: 'admin'
} as const;

const user: {
  readonly name: 'John',
  readonly role: 'admin'
};

const list = ['one', 'two', 3, 4];

const list = ['one', 'two', 3, 4] as const;

readonly ['one', 'two', 3, 4]

const colors = [
  { color: 'red', code: { rgb: [255, 0, 0], hex: '#FF0000' } },
  { color: 'green', code: { rgb: [0, 255, 0], hex: '#00FF00' } },
  { color: 'blue', code: { rgb: [0, 0, 255], hex: '#0000FF' } },
] as const;

const colors: readonly [
    {
        readonly color: 'red';
        readonly code: {
            readonly rgb: readonly [255, 0, 0];
            readonly hex: '#FF0000';
        };
    },
    /// ...
]

Ringkasan