Consolé esta palabra clave (consulte el código) pero para div, la salida de la consola era diferente y para la etiqueta de entrada es diferente. ¿Preguntándome por qué?

 (function(){ document.addEventListener('DOMContentLoaded', function(){ const complement = new Complement(); complement.generateRandomNumber(); complement.events(); }); class Complement{ constructor(){ this.firstInt = document.getElementById('firstint') //this is div this.secondInt = document.getElementById('secondint') //this is input this.sumInt = document.getElementById('sumint') } events = function(){ this.secondInt.addEventListener('keyup', this.checkFields) } } Complement.prototype.generateRandomNumber = function(){ **console.log(this) //this refers to the Class Complement. why?** let randonFirstInt = Math.floor(Math.random()*100) //assign random number to first integer this.firstInt.textContent = randonFirstInt; } Complement.prototype.checkFields = function() { **console.log(this) //this refers to the input tag. why?** let secondIntInput = this.value console.log(secondIntInput) }

})()