lesson 12: Object Type Tool Belt

typeof

const defaultOrder = {
    articles: [
        {
            price: 1200.50,
            vat: 0.2,
            title: 'Macbook Air Refurbished - 2013'
        },
        {
            price: 9,
            vat: 0,
            title: 'I feel smashing subscription'
        }
    ],
    customer: {
        name: 'Fritz Furball',
        address: {
            city: 'Smashing Hill',
            zip: '90210',
            street: 'Whisker-ia Lane',
            number: '1337'
        },
        dateOfBirth: new Date(2006, 9, 1)
    }
}

我们有一个复杂的对象，想把这个对象作为一个通用的类型，为了不写冗长的类型声明，我们可以使用typeof提取对象类型

type Order = typeof defaultOrder
function checkOrders(orders: Order[]) {
    let valid = true;
    for (let order of orders) {
        valid = valid && order.articles.length > 0
    }
    return valid
}

如果你更新了对象defaultOrder，类型Order也会跟着更新

Optional Properties

如果我们希望一个对象的属性是可选的，则使用问号？

type Article = {
    title: string,
    price: number,
    vat: number,
    stock?: number,
    description?: string
}

Exporting and Importing Types

如果我们不想重复声明类型，可是使用module
导出类型

export type Article = {
  title: string,
  price: number,
  vat: number,
  stock?: number,
  description?: string
}

导入类型

import { Article } from './example-two'
  const book: Article = {
  price: 29,
  vat: 0.2,
  title: 'Another book by Smashing Books'
}

如果我们只对类型感兴趣，可以在import后加上type

import type { Article } from './example-two'
  const book: Article = {
  price: 29,
  vat: 0.2,
  title: 'Another book by Smashing Books'
}