You're right, extending the prototype of builtin objects is almost always a bad idea. See String.prototype.contains → String.prototype.includes because mootool

You're right, extending the prototype of builtin objects is almost always a bad idea. See String.prototype.contains → String.prototype.includes because mootools extended the String prototype[1] [1] - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/includes#String.prototype.contains https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...