Have a class:

'use strict'

class modal{
    modal_wnd;
    close;
    constructor(){
        this._init();
    }

    _init(){
        this.modal_wnd = document.getElementById('modal'); //div
        this.close = document.getElementById('mdl_close'); // span 'X'
        this.close.addEventListener('click', this.close_1);
    }

    show(){
        this.modal_wnd.style.visibility = 'visible';
    }

    close_1(){
        alert(this.close);
        this.modal_wnd.style.visibility = 'hidden';
    }
}

Have div-element 'modal' and span 'X' in it. On a page have a button to show div:

bt_modal.addEventListener("click", function(){
                    let mdl = new modal();
                    mdl.show();
                });

that works fine, but when I press 'X' - get such an error: Uncaught TypeError: Cannot read properties of undefined (reading 'style') at HTMLSpanElement.close_1. Can anyone explain why does it happen?