text: function concat(str1,str2){
      if(str1){
        if(str2){
          if(typeof(str1) == "string" && typeof(str2) == "string"){
            console.log(str1+str2);
          }else{
            throw("not string")
          }
        }else{
          throw("Second argument is not defined")
        }
      }
      else if(str2){
        throw("First argument is not defined")
      }
      else{
        throw("Both arguments are not defined")
      }
      
    }
  
  try{
      concat("a","b") // "ab"
  }catch(e){
      console.log(e)
  }
  
  try{
      concat("a") 
  }catch(e){
      console.log(e) // Second argument is not defined
  }
  
  try{
      concat(1,"c") 
  }catch(e){
      console.log(e) // not string
  }
  
  try{
      conact(undefined,"x") 
  }catch(e){
      console.log(e) // First argument is not defined
  }
  
  try{
      concat() 
  }catch(e){
      console.log(e) //Both arguments are not defined
  }
  