inherits

inherits.js

function inherits(Child, Parent) {
    let F = function(){}
    // F only inherits Parent method, not instance property
    F.prototype = Parent.prototype
    Child.prototype = new F()
    Child.prototype.constructor = Child;
}

// Usage
function Student(props) {
    this.name = props.name || 'Unnamed';
}

Student.prototype.hello = function () {
    alert('Hello, ' + this.name + '!');
}

function PrimaryStudent(props) {
    Student.call(this, props);
    this.grade = props.grade || 1;
}

// inherits must write before PrimaryStudent.prototype, otherwise will be rewrited
inherits(PrimaryStudent, Student);

PrimaryStudent.prototype.getGrade = function () {
    return this.grade;
};