I was refactoring my code today to make it more efficient and suddenly a question popped into my mind. Which is more efficient and which is the best practice that can be used in any language or framework?

Approach-1

 for(let i=0;i<testList;i++){
      let reusedVar = testList[i];
        let testData= {
            firstName: reusedVar.firstName,
            lastName: reusedVar.lastName,
            ....
       }
     this.testTableData.push(testData);
     this.dataSource = new MatTableDataSource(this.testTableData);
 }

Approach-2

 for(let i=0;i<testList;i++){
  let testData= {
       firstName: testList[i].firstName,
       lastName: testList[i].lastName,
       .....
   }
 this.testTableData.push(testData);
 this.dataSource = new MatTableDataSource(this.testTableData);
}

Which approach from above is more efficient and why?

Thanks in advance.