JSFiddle - React, Tailwind, and code Playground

HTML

<button type="button">click</button>

JavaScript

Function.prototype.addMethod = function(name, fn){
	this[name] = fn;
}

var methods = function(){}

var methods1 = new Function();

methods.addMethod('checkName', function(){
	alert(1);
});

methods.addMethod('checkEmail', function(){
	alert(2);
});

methods.checkName();