if I have a javascript ES6 class like this:

import $ from jquery; 



export class test {



  constructor() {

    this.es6 = 'yay';

  }



  writeLine(text){

    console.log(text);

  }



  getTestData(){

    writeLine('writeLine call'); // <-- can not call writeLine ??

    $.get('/test', function(data){

        console.log(data);

        console.log(data.data);

        this.es6 = data.data;

        debugger

        writeLine(data.data);

    });

 }

} 

From another file I import the class and call getTestData

System.import('app/classDefinition')

.then(function(classDefinitionModul) {

   var test = new classDefinitionModul.test();

   console.log(test.es6);

   test.getTestData();

})

How can I call the method writeLine??