loop in checked value angular 4

i need to send every employee i checked to postCouncilAbsence function parameter, i want to make a loop to loop each employee i checked then send him as parameter .. any help using typescript?

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component.ts:

onattendanceSave(form:NgForm){
    this.index = this.attendanceForm.value
    console.log(this.index);
    Object.keys(this.index).forEach( key => {
    this.dataStorageService.postCouncilAbsence(this.index,this.Id)
    .subscribe(
        response => {
            console.log('save'+ this.index);
        }),
        error =>{ 
            console.log('error');
        }
  });
}
onChange(attendance:string, isChecked: boolean) {
    const attendanceFormArray = 
    <FormArray>this.attendanceForm.controls.isAttend;
    if(isChecked) {
        attendanceFormArray.push(new FormControl(attendance));
    } else {
      let index = attendanceFormArray.controls.findIndex(x => x.value == attendance)
      attendanceFormArray.removeAt(index);
    }
}

component.html:

<form [formGroup]="attendanceForm" >
 <div class="row">
    <table class="table table-hover table-condensed text-center table-bordered">
        <thead>
            <tr>
               <th> attendances </th>
               <th> check </th>
             </tr>
         </thead>
         <tbody>
          <tr *ngFor="let attendance of attendances"  >
             <td hidden></td>
             <td >  </td>
              <td> 
                <div class="form-check">
                    <label class="form-check-label">
                      <input type="checkbox (change)="onChange(attendance.Employee_ID,$event.target.checked)" >                                                                              
                    </label>
                </div>
              </td>
            </tr>
        </tbody>
     </table>
   </div>
  <div class="modal-footer">
      <button type="submit" class="btn btn-success" (click)="onattendanceSave(attendanceForm.value)"> save </button>
  </div>
  </form>