Can someone please let me know where I'm messing up in the code?

class Student {
    constructor(gpa, credits){
        this.gpa = gpa;
        this.credits = credits;
    }

    stringGPA() {
        return this.gpa.toString();
    }

    get level() {
        if (this.credits > 90 ) {
            return 'Senior';
        } else if (this.credits > 60) {
            return 'Junior';
        } else if (this.credits > 30) {
            return 'Sophomore';
        } else {
            return 'Freshman';
        }
    }

  set major(major) {

    this._major = 'major';

    if (this.credits === 'Senior' || this.credits === 'Junior' ) {
      return this._major;
    }

    else {
      this._major = 'none';
      return this._major;


    }




  }


}

var student = new Student(3.9, 60);