Typescript TS basic knowledge and so on

1. Use keywords class Define a class

class Person { }

2. Define instance properties in the class

adopt new The instance object generated by the call can access

class Person{

  name:string = ' name '

  age:number = 18

}

const per = new Person()

console.log(per.name)

3. static Class properties / Static attribute

adopt 【 Class name . Property name 】 visit , Use keywords static modification , There is no need to create an instance to use , Instance object cannot be read

class Person{

  name:string = ' name '

  staticage:number = 18

}

const per = new Person()

console.log(per.name, Person.age)

4. readonly Read-only property

class Person{

  readonly name:string = ' name '

  static readonly age:number = 18

}

5. Define methods

Example method Medium this Represents the object that currently invokes the method

class Person{
  say123(){ console.log(123)
  static say456(){ console.log(123)
}
const per = new Person()
per.say123()
Person.say456()

6. constructor Constructors

Constructors are created on objects （new call ） Called when the , Function this Represents the currently created instance object

class Person{
  name:string
  age:number
  constructor(name:string, age:number){
    this.name = name
    this.age = age
  }
}
const ming = new Person(' Xiao Ming ', 16)
const fang = new Person(' Xiaofang ', 18)

7. extends Inherit

class Subclass extends Parent class { }

After using inheritance , The subclass will have all the methods and properties of the parent class ; By inheritance , We can write code common to multiple classes in a parent class , In this way, you only need to write once to make all subclasses have properties and methods in the parent class at the same time

If you want to add unique attributes or methods to subclasses , Just write it directly . If a method with the same name in the parent class is added to the subclass , Then the subclass method will override the method in the parent class , We call it Method rewriting .

class Animal{
  name:string
  age:number
  constructor(name:string, age:number){
    this.name = name
    this.age = age
  }
  sayHi(){
    console.log(' The animal barks again !')
  }
}
class Dog extends Animal{
  run(){
    console.log(this.name+' Running ~')
  }
}
class Cat extends Animal{

}
const cat = new Cat(' kitten ', 2)
const dog = new Dog(' puppy ', 3)
dog.run()
// cat.run() // Report errors 
cat.sayHi()

Reference the parent method in the subclass method , use super Keyword indicates the parent class of the current class

class Dog extends Animal {

    sayHi(){ super.sayHi() }

}

If you write constructor Constructors , You need to call the constructor of the parent class in the subclass constructor ,super()

class Animal{

  name:string

  constructor(name:string){  this.name = name }

}

class Dog extends Animal{

  age:number

  constructor(name:string, age:number){

    super(name)

    this.age = age

  }

}

8. abstract  abstract class

With abstract The class starting with the keyword is an abstract class , Is a special class for inheritance , Can't be used to create objects

Abstract methods can be added to abstract classes , Define only the structure , Do not define specific implementation . Abstract methods can only be defined in abstract classes , Subclasses must override abstract methods

abstract class Animal{

  name:string

  constructor(name:string){

    this.name = name

  }

  abstract sayHi():void

}

class Dog extends Animal{

  sayHi(): void { ... }

}