JSFiddle - React, Tailwind, and code Playground

JavaScript

var variable ="myStrinG";
var newArray=[]
var getArray = variable.split('');
getArray.forEach(function(item){
 if(item == item.toUpperCase()){
    var conCharacter = item.toLowerCase();
    newArray.push(conCharacter);
 }
else{ 
   var conCharacter = item.toUpperCase();
   newArray.push(conCharacter);
}
})
var getNewString = newArray.join('')
document.write('<pre>'+getNewString+'</pre>')