JSFiddle - React, Tailwind, and code Playground

HTML

<button id="id">Button</button>

JavaScript

var Foo = (function(){
    
    function Foo(){
        this._s="string";
        this.setButton();
    };
    
    Foo.prototype.setButton = function(){
document.getElementById('id').addEventListener('click',	function(event) {
            alert(this._s);
		});
    };
    
    Foo.prototype.method = function(){
        alert(this._s);
    };
    
    return Foo;
    
})();

var fo = new Foo();
fo.method();