why array.map returns undefined 1

why array.map returns undefined

let test = [ {name:'test',lastname:'kumar',age:30},
             {name:'test',lastname:'kumar',age:30},
             {name:'test3',lastname:'kumar',age:47},
             {name:'test',lastname:'kumar',age:28},
             {name:'test4',lastname:'kumar',age:30},
             {name:'test',lastname:'kumar',age:29}]

let result1 = test.filter(element => 
              { 
                 if (element.age === 30) 
                 {
                    return element;
                 }
              }).map(({lastname})=>lastname)
console.log(result1);
output : ['kumar','kumar','kumar']

Here is what the above code is Doing:
1. First, we are filtering the array based on the age.
2. Then, we are mapping the lastname of the filtered array.

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