Why can't I access the level() getter methods' output?

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';
        }
    }
    // why won't this work?
    set major() {
        if (this.level === 'Senior' || this.level === 'Junior' ) {
            _major = major;
        } else if (this.level === 'Sophomore' || this.level === 'Freshman' ) {
            _major = 'None';
        }
    }
}