Why does data in my JavaScript class is undefined when calling it from a component?

I have in an external JavasScript (sun.js) file a class like this :

export default class Sun {
   constructor(){
      this.text = 'I'm shining!';
   }
    
    static testIfShining() {
       console.log("is the sun shining?");
       console.log(this.text);
    }
 }

So I’m importing this class in one of my component

import Sun from '../sun.js'

And then I call my function testIfShining() in my mounted lifecycle :

mounted() {
   Sun.testIfShining();
}

When I look at my console, I have the message log

is the sun shining?
undefined

The function is working but I have an undefined value for the data this.text

How can I reuse the value inside my constructor? I want to my data works like attribute so I can reuse it in every function in my class.

Answer

If you write/copy your code well here you have to escape the single quote. Like

 this.text = 'I'm shining!';

in your code

export default class Sun {
   constructor(){
      this.text = "I'm shining!"; // <------- Use also double quote
   }
    
   testIfShining() { // <------ remove the static
       console.log("is the sun shining?");
       console.log(this.text);
    }
 }

edit: Reply to fast. And also use like this :

Could you try this

mounted() {
   let sun = new Sun();
   sun.testIfShining();
}

example: https://jsfiddle.net/y4675twv/2/