javascript class static method

1// Classes : static methods in javascript classes 
2
3class Square {
4    constructor(width){
5        this.width = width ;
6        this.height = width ;
7    }
8
9    static equals(a , b){
10        return a.width * a.height === b.width * b.height ;
11    }
12
13    static validDimensions(width , height ){
14        return width === height ;
15    }
16}
17
18console.log(Square.validDimensions(8 , 8));
19console.log(Square.validDimensions(10 , 12));
20console.log(Square.validDimensions(0 ,0 ));
21console.log(Square.validDimensions(2 , 3));
22console.log(Square.validDimensions(-3 , -3));

1class ClassWithInstanceField {
2  instanceField = 'instance field'
3}
4
5class ClassWithStaticField {
6  static staticField = 'static field'
7}

1class myClass{
2 
3constructor(){
4this.myLocaleVariable=1;//this.varname in the constructer function makes a locale var
5}
6localfunction(){
7return "im local unique to this variable";
8}
9static publicfunction(){
10return "i can be called without an obj"
11}
12  
13}
14myClass.myPublicVariable = 0;
15
16
17
18myClass.localfunction();//error
19myClass.publicfunction();//"i can be called without an obj"
20myClass.myLocaleVariable;//error
21myClass.myPublicVariable;//0
22var obj = new myClass;
23obj.localfunction();//"im local unique to this variable"
24obj.publicfunction();//error
25obj.myLocaleVariable;//1
26obj.myPublicVariable;//error
27

1class Hi {
2	constructor() {
3      console.log("hi");
4    }
5   	my_method(){}
6  	static my_static_method() {}
7}
8
9function getStaticMethods(cl) {
10  return Object.getOwnPropertyNames(cl)
11}
12
13console.log(getStaticMethods(Hi))
14// => [ 'length', 'prototype', 'my_static_method', 'name' ]
15

1// *** JS Class STATIC method ***   
2
3class Animal {
4        sayHello() {
5            return `${this.constructor.greeting}! I'm ${this.name}!`;
6        }
7    }
8
9    class Cat extends Animal {
10        constructor(name) {
11            super(); // connects parent to child/constructor
12            this.name = name; //=> need this line otherwise name undefined
13        }
14        static greeting = 'Feed me';
15    }
16
17    class Dog extends Animal {
18        constructor(name) {
19            super();
20            this.name = name; // same output type as above
21        }
22        static greeting = 'Sigh';
23    }
24
25    const run = document.getElementById("run");
26    run.addEventListener('click', () => {
27        let Garfield = new Cat('Garfield');
28        let Snoopy = new Dog('Snoopy');
29        console.log(Garfield.sayHello());
30        console.log(Snoopy.sayHello());
31    })
32// output = Feed me! I'm Garfield! Sigh! I'm Snoopy!

1class ClassWithStaticMethod {
2  static staticMethod() {
3    return 'static method has been called.';
4  }
5}
6
7console.log(ClassWithStaticMethod.staticMethod());
8// expected output: "static method has been called."
9