text: function viewNumber(num,callback) {
    console.log(num);
    callback();
  }
  
  viewNumber(2,function(result){
    console.log(result);
    viewNumber(4,function (result) {
        console.log(result);
        viewNumber(6,function (result) {
            console.log(result);
            viewNumber(8,function (result) {
                console.log(result);
                viewNumber(10,function (result) { 
                    console.log(result);       
    });
        
    });
    });
    });
  })