JSFiddle - React, Tailwind, and code Playground

JavaScript

var t = 'aaaBBB';
var t2 = ''
var t2 = t.split('')

var res = t2.map(function(name){
	 if(name==name.toUpperCase()){
   	return name.toLowerCase()
   }
   
    if(name==name.toLowerCase()){
   	return name.toUpperCase()
   }
})

console.log(res)