手を動かしながら学ぶ TypeScript Part 1 -- 基礎的な型

const name: string = 'Aki' const age: number = 20 

const dog : { name: string, age: number, } = { name: 'Aki', age: '300', } 

const dogAge: number = 3 const dog: { age:number } = { age: 3} 

obj.ts:15:3 - error TS2322: Type 'string' is not assignable to type 'number'. 15 age: '300', ~~~ obj.ts:12:3 12 age: number, ~~~ The expected type comes from property 'age' which is declared here on type '{ name: string; age: number; }' 

const isOpen: boolean = true 

tsc bool.ts bool.ts:3:7 - error TS2322: Type 'string' is not assignable to type 'boolean'. 3 const empty: boolean = '' ~~~~~ bool.ts:4:7 - error TS2322: Type 'number' is not assignable to type 'boolean'. 4 const zero: boolean = 0 ~~~~ bool.ts:5:7 - error TS2397: Declaration name conflicts with built-in global identifier 'undefined'. 5 const undefined: boolean = undefined ~~~~~~~~~ bool.ts:5:28 - error TS2448: Block-scoped variable 'undefined' used before its declaration. 5 const undefined: boolean = undefined ~~~~~~~~~ bool.ts:5:7 5 const undefined: boolean = undefined ~~~~~~~~~ 'undefined' is declared here. Found 4 errors. 

const list: number[] = [0, 1, 2, ] list.push(99) list.push('text') 

tsc arr.ts arr.ts:3:11 - error TS2345: Argument of type 'string' is not assignable to parameter of type 'number'. 3 list.push('text') ~~~~~~ 

const numList: Array<number> = [1, 2, 3, false, ] 

const text: string = 'text' const undefString: string = undefined const nullString: string = null 

{ "compilerOptions": { "target": "es5", /* Strict Type-Checking Options */ "strict": true, /* Enable all strict type-checking options. */ "strictNullChecks": true, /* Enable strict null checks. */ 

let text: string = 'text' text = undefined text = null 

type hoge:string; export const foo:hoge => { ... } 

const baby : { name: string, weightGrams: number, } = { name: "Taro", weightGrams: 300, } baby.name = 'smile' 

const woman : { readonly name: string, age: number, } = { name: 'Aki', age: 25, } woman.age = 80 woman.name = 'Teru' 

tsc ro.ts ro.ts:20:7 - error TS2540: Cannot assign to 'name' because it is a read-only property. 20 woman.name = 'Teru' 

interface Person { name: string, power: number, } const kaede: Person = { name: 'kaede', power: 70, } 

function App() { interface cat { color: string; weight: number; } const Tama:cat = { color: 'white', weight: 5000, } return ( <div> <h2>{Tama.weight}</h2>  </div>  ); }