findUnique.js

const findSingle = (arr) => {
  
  let obj = {}
  
  for(let item of arr ){
    
    if(obj[item]{
      obj[item]+= 1
     }else{
       obj[item] = 1
     }
   }
       
  for(let item in obj){
    if(obj[item] === 1){ 
      return item
    }
  }
}