What is better use in Angular2 (local variable or get or set class on div)?

Question

For example:

First example with variable.

    ` <div id="loader" class="" *ngif="isLoader"></div>  ` 
    isLoader:boolean=false; 

    onLoad(){           
        isLoader=true;

        this.http.get('localhost/data').subscribe( 
             res=>{
               console.log(res.json());
               isLoader=false;   
             } 
        }
    }

Next example with set class on div

    ` <div id="loader" class=""></div>  `
    onLoad(){
         document.getElementById("loader").className = "loader";

         this.http.get('localhost/data').subscribe( 
            res=>{
               console.log(res.json());
               document.getElementById("loader").className = "";
            } 
         }
    }

Which example is better.