allPossibleCombinations.js

et string = "abcfed";
let splited  = string.split('');
 
 
  let str2 = "";
  let str1 = "" ; 
  let str3 = "";  
  const obj = {};

    for(let i = 0; i < splited.length ; i++){
            
              str1 += splited[i]
              obj[splited[i]] = true;
              obj[str1] = true;
          
              for(let b = i+1 ;b < splited.length; b++){
                  str2 = splited[i] +  splited[b] ;
                  str3 += splited[b];                            
                  obj[str2] = true;
                  obj[str3]= true;                

              }     
              str3="";      
    }
   
  

console.log(Object.keys(obj))

first