SOURCE

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))