test.ts

class Course{
    constructor(private _id:number,private _name:string){

    }
    get id(){
        return this._id
    }
    set id(id:number){
        this._id=id
    }
}
class School {
    private courses:Course[]
    constructor(private _name:string){
        this.courses = []
    }
    get name(){
        return this._name
    }
    set name(name:string){
        this._name=name
    }
    addCourse(course:Course):void{
        this.courses.push(course)
    }
}

class University extends School{
    constructor(name:string,private web:string){
        super(name)
    }
}
let school:University

school = new University('U','u.com')
school.addCourse(new Course(1,'JS'))
console.log(school)