JSFiddle - React, Tailwind, and code Playground

JavaScript

function tomath2 (arg1,arg2) {
	for (var i=0; i<arg1.length; i++) {
		if (arg2=="round") {
			arg1[i]=Math.round(arg1[i]);
			document.write(arg1[i] + "<br>"); 
		} 
		else if (arg2=="ceil") {
			arg1[i]=Math.ceil(arg1[i]);
			document.write(arg1[i] + "<br>"); 
		}
		else if (arg2=="floor") {
			arg1[i]=Math.floor(arg1[i]);
			document.write(arg1[i] + "<br>"); 
		}
		else {
			document.write("<strong> Неверный метод </strong><br>");
		};
	};
	//return arg1;
};

var numberArray = [34.82, 12.90, 17.01, 78.51];
var metod1 = "round";
var metod2 = "ceil";
var metod3 = "floor";

document.write(numberArray + "<strong> Изначальное значение </strong><br><br>"); 

tomath2(numberArray,metod1);
document.write("<br>");
tomath2(numberArray,metod2);
document.write("<br>");
tomath2(numberArray,metod3);
document.write("<br>");