typescript学习笔记-基础类型

基础类型快速入门

基础类型 string,number,boolean

const teacher:string = 'Li';
const age:number = 18;
const isMale:boolean = true;

数组类型 string,number,boolean

const arr:number[] = [1,2,3]  // 数字类型数组
const arr:string[] = [1,2,3]   // 字符串类型数组
const boolArr:Array = [true,false]  // 传参形式定义布尔数组，范型

对象类型

const user:{name:string,age:number} = {name:'Li',age:18}
const userOne:{name:string,age?:number} = {name:'Li'}  // ?表示age可有可无

联合类型 Union Type |

function union(id:string|number){
  if (typeof id === 'string') {  // 类型收窄 Narrowing
      console.log(id.toUpperCase())
  } else {
      consle.log(id)
  }
}

any类型

function showMessage(msg:any){
  console.log(msg)
}

函数类型

function fn(msg:string):number { // 返回值number类型
  return 123
}

const def:(age:number) => number = (age:number) => { return 18}

类型别名,类型复用

type:User = {name:string,age:number}
type:Employee = {name:string,age:number,salary:number}
const userTwo:User = {name:'Li',age:18}
const userThree:User = {name:'Li',age:18}

接口类型 Interface

interface Student {
  age:number;
  sex?:string;
}
// 写法1
interface Student {
  name: string
}
// 写法2
interface oldStudent extends Student {
  name: string
}
const student:Student = {age:18,sex:'male'}
const oldStudent:oldStudent= {age:18,sex:'male',name:'Li'}

interface 类型跟类型别名类似，区别在于。接口类型具有可扩展性可以继承,一般都是尽量用interface

交叉类型

type:User = {name:string,age:number}
type:Employee = User && {salary:number} // 交叉类型

const employee: Employee = {name:"Li",age:18,salary:1000}

断言 Assersion(绕过ts检测，按我们的意思来)

const dom:undefind = document.getElementById('root') as undefind
const dom1:undefind = document.getElementById('root') 
const testString:string = 123 as any as string

字面量类型

const str:'abc' = 'abc'  // 只能类型,值一样

function getPosition(position:'left' | 'right') { // 传参只能是left或者 right
  return position
}
getPosition('left')
getPosition('right')

null undefind tsconfig

const testNull:null = undefind // ts不严谨  需配置 `"strictNullChecks": true`
const testundefind:undefind = null // ts不严谨  需配置 `"strictNullChecks": true`
function checkNull(abc:string | null){
  if (typeof abc === 'string') {
      console.log(abc!.toUpperCase()) // !表示可以确定只会是string类型，不会有null
  }
}

void 函数没有返回值

function getNumber():void{

}