JSFiddle - React, Tailwind, and code Playground

JavaScript

var madrobby=function(a,b,c,d,e,f,g,h,i,j,k,l,m){return b=a%19,c=~~(a/100),d=a%100,e=~~(c/4),f=c%4,g=~~((c+8)/25),h=~~((c-g+1)/3),i=(19*b+c-e-h+15)%30,j=~~(d/4),k=d%4,l=(32+2*f+2*j-i-k)%7,m=~~((b+11*i+22*l)/451),a+"-"+~~((i+l-7*m+114)/31)+"-"+((i+l-7*m+114)%31+1)}


var jsjohnst=function(y,a,b){return a=~~(y/100),b=(19*(y%19)+a-~~(a/4)-~~((a-~~((a+8)/25)+1)/3)+15)%30,a=(32+2*(a%4)+2*~~(y%100/4)-b-y%100%4)%7,a=-(b+a-7*~~((y%19+11*b+22*a)/451)+114),''+y+~~(a/31)+(a%31-1)}


document.body.innerHTML = "<br><br>";

document.body.innerHTML += madrobby.toString().replace(/ /g, "").replace(/return/, "return ") + "<br><br>";
document.body.innerHTML += "Thomas Fuchs: <b>" + (madrobby.toString().replace(/ /g, "").length+1) + "</b>";

document.body.innerHTML += "<br><br><br>";

document.body.innerHTML += jsjohnst.toString().replace(/ /g, "").replace(/return/, "return ") + "<br><br>";
document.body.innerHTML += "Jeremy Johnstone: <b>" + (jsjohnst.toString().replace(/ /g, "").length+1) + "</b>";

document.body.innerHTML += "<br><br><br>";

function check() {
   for(var i=33;i<10000;i++) {
       if(madrobby(i) != jsjohnst(i)) {
           document.body.innerHTML += "Not match: " + i;
           return;
       }
   }
   document.body.innerHTML += "Match for all years!";
}

check();