typescript_program

 13 + [] // Error TS2365: Operator '+' cannot be applied to types '3' and 'never[]'.
 2
 3
 4let obj = {}
 5obj.foo // Error TS2339: Property 'foo' does not exist on type '{}'
 6
 7function (a: number) {
 8  return b / 2
 9}
10a('z') // Error TS2345: Argument of type '"z"' is not assignable to parameter of type 'number'.

1// 显示注解
2let a: number = 1
3let b: string = 'hello'
4let c: boolean[] = [true, false]
5
6// 自动推导
7let a = 1;
8let b = 'hello'
9let c = [true, false]

1// example
2let a: unknown = 30; // unknown
3let b = a === 123; // boolean
4let c = a + 10; // Error TS 2571: Object is of type 'unknown'
5if (typeof a === 'number') {
6  let d = a + 10; // number
7}

1// example
2let a = true                // boolean
3let b = false               // boolean
4const c = true              // true
5let d: boolean = true       // boolean
6let e: true = true          // true
7let f: true = false         // Error TS2322: Type 'false' is not assignable to type 'true'.

1// example
2let a = 1234                  // number
3let b = Infinity * 0.1        // number
4const c = 5678                // 5678
5let d = a < b                 // boolean
6let e: number = 100           // number
7let f: 26.218 = 26.218        // 26.218
8let g: 26.218 = 10            // Error TS2322: Type '10' is not assignable to type '26.218'

1let oneMillion = 1_000_ 000    // 等同于 1000000
2let twoMillion: 2_000_000 = 2_000_000

1// example
2let a = 1234n                  // bigint
3const b = 5678n                // 5678n
4let c = a + b                  // bigint
5let d = a < 1235               // boolean
6let e = 88.5n                  // Error TS1353: A bigint literal must be an integer.
7let f: bigint = 100n           // bigint
8let g: 100n = 100n             // 100n
9let h: bigint = 100            // Error TS2322: Type '100' is not assignable ty type 'bigint'.

1// example
2let a = 'hello'                 // string
3let b = 'billy'                 // string
4const c = '!'                   // !
5let d = a + ' ' + b + c         // string
6let e: string = 'zoom'          // string
7let f: 'john' = 'john'          // john
8let g: 'john' = 'zoe'           // Error TS2322: Type 'zoe' is not assignable to type 'john'

1// example
2let a = Symbol('a')              // symbol
3let b: symbol = Symbol('b')      // symbol
4let c = a === b                  // boolean
5let d = a + 'x'                  // Error TS2469: The '+' operator cannot be applied to type 'symbol'.

1// example
2const e = Symbol('e')                  // unique symbol
3const f: unique symbol = Symbol('f')   // unique symbol
4let g: unique symbol = Symbol('f')     // Error TS1332: A variable whose type is a 'unique symbol' type must be 'const'.
5let h = e === e                        // boolean
6let i = e === f                        // Error TS2367: This condition will always return 'false' since the type 'unique symbol' and 'unique symbol' have no overlap.

1// example
2let b: object = {
3  b: 'x'
4}
5a.b // Error TS2339: Property 'b' does not exist on type 'object'.

 1// 对象字面量
 2
 3// 自动推导
 4let a = {
 5  b: 'x'
 6}
 7
 8// or
 9let a: { b: string } = {
10  b: 'x'
11}

1let a: { b: number }
2b = {} // Error TS2741: Property 'b' is missing in type '{}' but required in type '{b: number}'.
3
4b = {
5  a: 1,
6  b: 2
7} // Error TS2322: Type '{b: number; c: number}' is not assignable to type '{b: number}'. Object literal may only specify known properties, and 'c' does not exist in type '{b: number}'.

1let a: {
2  b: number
3  c?: string        // 可能有个类型为 string 的属性 c。其值可以为 undefined
4  readonly firstName: string // 为字段赋初始值后无法修改。类似于使用 const 声明对象的属性
5  [key: number]: boolean // 可能有任意多个数字属性，其值为布尔值
6}

 1type Age = number
 2
 3type Person = {
 4  name: string
 5  age: Age
 6}
 7
 8let driver: Person = {
 9  name: 'Jack'
10  age: 18
11}

 1type Cat = { name: string, purrs: boolean }
 2type Dog ={ name: string, barks: boolean, wags: boolean }
 3
 4type CatOrDogOrBoth = Cat | Dog // 并集
 5type CatAndDog = Cat & Dog // 交集
 6
 7// CatOrDogOrBoth 可以是 Cat 类型的值，可以是 Dog 类型的值，还可以二者兼具。
 8// Cat
 9let a: CatOrDogOrBoth = {
10  name: 'Bonkers',
11  purrs: true
12}
13
14// Dog
15a = {
16  name: 'Domino',
17  barks: true,
18  wags: true
19}
20
21// 二者兼具
22a = {
23  name: 'Donkers',
24  barsk: true,
25  purrs: true,
26  wags: true
27}
28
29// CatAndDot
30let b: CatAndDog = {
31  name: 'Domino',
32  barks: true,
33  purrs: true,
34  wags: true
35}

 1let a = [1, 2, 3]                // number[]
 2let b = ['a', 'b']               // string[]
 3let c: string[] = ['a']          // string[]
 4let d = [1, 'a']                 // (number | string)[]
 5const e = [2, 'b']               // (number | string)[]
 6let f = ['red']                  // string[]
 7
 8f.push('blue')
 9f.push(true)                     // Error TS2345: Argument of type 'true' is not assignable to parameter of type 'string'.
10
11let g = []                       // any[]
12g.push(1)                        // number[]
13g.push('red')                    // (number | string)[]
14
15let h: number[] = []             // number[]
16h.push(1)                        // number[]
17h.push('red')                    // Error TS2345: Argument of type '"red"' is not assignable to parameter of type 'number'.

1let a: [number] = 1
2let b: [string, string, number] = ['jack', 'boy', 1963]
3b = ['tom', 'boy', 'li', 1926] // Error TS2322: Type 'string' is not assignable to type 'number'.

 1let trainFares: [number, number?][] = [
 2  [3.75],
 3  [8.25, 7.70],
 4  [10.60],
 5]
 6
 7// 等价于
 8let moreTrainFares: ([number, number] | [number])[] = [
 9  // ...
10]

1// 字符串列表，至少有一个元素
2let friends: [string, ...string[]] = ['Sara', 'Tali', 'Chloe', 'Claire']
3
4// 元素类型不同的列表
5let list: [number, boolean, ...string[]] = [1, false, 'a', 'b', 'c']

 1let as: readonly number[] = [1, 2, 3]     // readonly number[]
 2let bs: readonly number[] = as.concat(4)  // readonly number[]
 3let three = bs[2]                         // number
 4as[4] = 5                                 // Error TS2542: Index signature in type 'readonly number[]' only permits reading.
 5as.push(6)                                // Error TS2339: Property 'push' does not exist on type 'readonly number[]'.
 6
 7// Readonly 和 ReadonlyArray 句法
 8type A = readonly string[]                // readonly string[]
 9type B = ReadonlyArray<string>            // readonly string[]
10type C = Readonly<string[]>               // readonly string[]
11
12type D = readonly [number, string]        // readonly [number, string]
13type E = Readonly<[number, string]>       // readonly [number, string]

 1// 返回 never 的函数
 2function d() {
 3  throw TypeError('I always error')
 4}
 5
 6function e() {
 7  while (true) {
 8    doSomething()
 9  }
10}

1enum Language {
2  English,
3  Spaish,
4  Russian
5}

1enum Language {
2  English = 0,
3  Spanish = 1,
4  Russian = 2
5}

1let myFirstLanguage = Language.Russian
2let mySecondLanguage = Language['English']

1enum Language {
2  English = 0,
3  Spanish = 1,
4}
5
6enum Language {
7  Russian = 2
8}

1function add(a: number, b: number) {
2  return a + b
3}

1function add(a: number, b: number): number {
2  return a + b
3}

 1// 具名函数
 2function greet(name: string) {
 3  return 'hello ' + name
 4}
 5
 6// 函数表达式
 7let greet2 = function(name: string) {
 8  retunr 'hello ' + name
 9}
10
11// 箭头函数表达式
12let greet3 = (name: string) => {
13  return 'hello ' + name
14}
15
16// 箭头函数表达式简写
17let greet4 = (name: string) => 'hello ' + name
18
19// 函数构造方法
20let greet5 = new Function('name', 'return "hello " + name')

 1function log(message: string, userId?: string) {
 2  let time = new Date().toLocaleTimeString()
 3  console.log(time, message, userId || 'Not signed in')
 4}
 5
 6log('Page loded')
 7log('User signed in', 'da763be')
 8
 9// 默认值参数（类似可选参数功能
10function log(message: string, userId = 'Not signed in') { // userId 会自动推导类型
11  let time = new Date().toLocaleTimeString()
12  console.log(time, message, userId)
13}
14
15// 显式注解默认参数类型
16type Context = {
17  appId?: string
18  userId?: string
19}
20
21function log(message: string, context: Context = {}) {
22  let time = new Date().toLocaleTimeString()
23  console.log(time, message, context.userId)
24}

 1// example
 2function filter(array, f) {
 3  let result = []
 4  for (let i = 0; i < array.length; i++) {
 5    let item = array[i]
 6    if (f(item)) {
 7      result.push(item)
 8    }
 9  }
10  return result
11}
12
13filtre([1, 2, 3, 4], (item) => item < 3) // [1, 2]

 1type Filter = {
 2  (array: number[], f: (item: number) => boolean): number[]
 3  (array: string[], f: (item: string) => boolean): string[]
 4}
 5
 6// 加上对象类型
 7type Filter = {
 8  (array: number[], f: (item: number) => boolean): number[]
 9  (array: object[], f: (item: object) => boolean): object[]
10}

1// example
2type Filter = {
3  <T>(array: T[], f: (item: T): boolean): T[]
4}

 1// 1 在调用签名中声明
 2type Filter = {
 3  <T>(array: T[], f: (item: T): boolean): T[]
 4}
 5// 调用函数时为 T 绑定具体类型
 6let filter: Filter = (array, f) => {
 7  // ...
 8}
 9
10
11// 2 在类型别名 Filter 中
12type Filter<T> = {
13  (array: T[], f: (item: T): boolean): T[]
14}
15// 使用 Filter 时显式绑定具体类型
16let filter: Filter<number> = (array, f) => {
17  // ...
18}

 1// 1
 2type Filter = {
 3  <T>(array: T[], f: (item: T): boolean): T[]
 4}
 5
 6// 2
 7type Filter<T> = {
 8  (array: T[], f: (item: T): boolean): T[]
 9}
10
11// 3 1 的简写
12type Filter = <T>(array: T[], f: (item: T): boolean): T[]
13
14// 4 2 的简写
15type Filter<T>( = array: T[], f: (item: T): boolean): T[]
16
17// 5 具名函数调用签名，每次调用 filter 时绑定举腿类型
18function filter<T>(array: T[], f: (item: T) => boolean): T[] {
19  // ...
20}