Basic types of data in TS

ts data type

ts Basic data type

After declaring the type , The type of variable cannot be changed

A vertical line | ： Express or , Used to connect multiple types （ Joint type ）

question mark ？ For optional

& To express and

Boolean type boolean

let bool:boolean=true

Numeric type number

let num:number=10

String type string

let str:string=" I don't know what a rich woman is like when I'm young , Mistake beauty for treasure "

undefined type

const und:undefined=undefined

null type

const nul:null=null

null and undefined Are subtypes of other types , Can be assigned to any type

An array type Array

let arr:number[]=[1,2,3]

let arr:Array<number>=[10,20,30]

let arr:Array<nunber|string>=["hello",100,200]

After the array definition , The data type inside must be consistent with that when defining the array , Otherwise, an error will be reported

A tuple type tuple

let yuanZu:[string,number,boolean,undefined]=['haha',10,true,undefined]

A tuple is ts New data types , It can be understood as fixed length , An array of fixed data types for each location

Enumeration type enum

  enum Color {
    red,
    blue,
    yellow,
  }

  let color = Color.red;
  console.log(color); //0
  console.log(Color[2]); // yellow
  
  enum Sex {
     male  = 1,
     Woman ,
  }
  console.log(Sex. male ); //1
  console.log(Sex[2]); // Woman 

Each element in the enumeration has a number , The default from the 0 Start , It's incremented 1; But we can also define it ourselves ,eg from 1 Start

Enumeration can get the number through the element , You can also get the corresponding element by number

Elements can be directly in Chinese , But we don't recommend writing like this

any type

  let anyType: any = 100;
  anyType = " The bright moon in front of the window , Get up and open a window ; Get a slap in the face , All the teeth fall out ";
  console.log(anyType);
  let a: any[] = [false, 666, "hello"];

It can be any type , To use , But there is no error prompt when compiling ; It's equivalent to using js grammar

unknown type

and any be similar , You can assign values of any type to variables ;

But if you copy this variable to a variable of a known type ,unknow Will report a mistake , and any Can't

  let unknowType: unknown;
  unknowType = 10;
  unknowType = "str";
  console.log(unknowType);
  let c = unknowType;
  let d = 12;
  d = unknowType;  //  This line will report an error , because d It has been inferred that it is a number , Can't be unknown Assigned to numeric type , And if it is     any If you don't, you won't report an error ,undefined,null,any Can be assigned to any type 

void type

  function doSomething(): void {
    const str: string = " As long as the rich woman holds , Move into the villa overnight ";
  }
  doSomething();
  
  //  to void assignment , It doesn't make much sense 
  //   let vo: void = null/undefined;

When a function is declared , Use after parentheses void, It means that the function has no return value ( It is also equivalent to function return undefined or null)

object type object

 interface Person {
    age;
    name;
    height;
  }

  function getFitResult(obj: Person): object | boolean {
    const singleMale = {
      name: "Luca",
      age: 24,
      height: 180,
    };

    if (singleMale.age - obj.age <= 5 && singleMale.height - obj.height < 15) {
      return singleMale;
    } else {
      return false;
    }
  }

  const re = getFitResult({ name: "Ari", age: 24, height: 168 });
  console.log(re);

let a:{name:“ The Monkey King ”}

let a={name:“ The Monkey King ”,age?:number}

let a={name:“luca”,[propName:string]:any} , There has to be name, There can also be other attributes of any type

Joint type union

let a:number|string=20
a="hello"

The representation can be one of many types

Form

type	example	describe
number	0,12,-20	Arbitrary number
string	“hello”	Any string
boolean	true/false	Boolean value true/false
Literal	Its own	Limiting the value of a variable is changing the literal value ; It's a bit like const, Once declared, it cannot be changed
any	*	Any type , Set to any, It is equivalent to turning off... For this variable TS, And js almost
unknown	*	Type safe any
void	Null value （undefined）	No value （ or undefined）; Mostly used for functions with no return value
never	No value	Cannot be any value , It can be used for function error
object	{name:“luca”}	Any object ;{} Used to specify which attributes are included in the object , Add Hello after attribute , Said the optional
array	[1,“fun”,true]	Any array
tuple	[4,5]	Tuples ,TS New type , Fixed length array
enum	enum{A,B}	enumeration ,TS New type
undefined	undefined	Subtypes of any type
null	null	Subtypes of any type

Other related concepts

Types of assertions

Tell compiler , I know what type it is , Know what you're doing

grammar ：

 Variable  as  type 
< type > Variable 

  function getLength(str: string | number) {
   Because the received parameters may be arrays , The numbers don't have length, Direct use will report an error , So use type assertion to solve 
    if ((<string>str).length) {
      //  If there is a length , So it's a string 
      return (str as string).length;
    } else {
      return str.toString().length;
    }
  }

Type inference

If the variable type is not specified , According to the assignment , Infer a type

If the declaration is assigned at the same time , that TS The variable type can be detected automatically ; So declare and assign values , You can omit the declaration of the type

Only declare , No copy , The parser will set it to any( Implicit any)

let a=100   Infer as number
let b   // Infer as any