let str = 'abbaca'
function reaa (str) {
let arr = []
let strArr = str.split('')
for(let index = 0 ;index<strArr.length;index++){
if(strArr[index] == strArr[index+1]){
arr.push(...strArr.splice(index+2))
return reaa(arr.join(''))
}else{
arr.push(strArr[index])
if(arr.length ==strArr.length){
return arr
}
}
}
}
console.log(reaa (str))