function combString(str){
     var lenStr = str.length;
     var result = [];
     var indexCurrent = 0;

     while(indexCurrent < lenStr){
         var char = str.charAt(indexCurrent);
         var x;
         var arrTemp = [char];

         for(x in result) {
             arrTemp.push(""+result[x]+char);
         }
         result = result.concat(arrTemp);

         indexCurrent++;
     }

     return result;
}

console.log(combString("abc"));