Calculate sum of element array ionic 2

[amine216]

Here I create a model

nbr: number;
// other variables

getNb() {
  // ...
  this.members = data.CourseHsCheval ;
if ( curent.CourseHsCheval.rang ==1) {
  this.nbr = this.members.reduce((previous, current) => {
    return previous + 1 ; }
  }, 0);
}