函数

function foo(num: number): number {
  return num
}

interface User {
  name: string,
  age: number
}

const fn1: (user: User) => User = (user: User): User => {
  return user
}

console.log(fn1({name: 'olu', age: 18}))

下面这个匿名函数遍历中会自动推断 x 为 string 类型 👇🏻

const strArr: string[] = ["Olu", "Cool"]

strArr.forEach(x => {
  x.toUpperCase()
})

函数重载

重载允许一个函数接受不同数量或类型的参数时，作出不同的处理

function fn (params: number): void
function fn (params: string): void
function fn (params: string | number): string | number {
  console.log(params)
  return params
}

let a: void = fn(1)