JSFiddle - React, Tailwind, and code Playground

JavaScript

function Test(x){
     this.a = x;
     this.b = undefined;
     this.c = undefined;
}
Test.prototype.init = function(d,e,f){
     this.a = d;
     this.b = e;
     this.c = f;
};

var testobj = new Test(4);
testobj.init(1,2,3);
alert(testobj.a);//1
alert(testobj.b);//2
alert(testobj.c);//3