use 'strict';
function Student(props) {
    if (!props) props = {};
    this.name = props.name || 'unnamed';
    this.age = props.age || 23;
    Student.prototype.hello = function() {
        return 'hello!,' + this.name;
    }
}

function PrimaryStudent(props) {
    Student.call(this, props);
    this.grade = props.grade || 0;
    PrimaryStudent.prototype.say = function() {
        return 'say!,' + this.name;
    }

}

function inherits(child, parent) {
    function F() {};
    F.prototype = parent.prototype;
    child.prototype = new F();
    child.prototype.constructor = child;
}

function inherits2(child, parent) {
    child.prototype = new parent();
    child.prototype.constructor = child;
}

inherits2(PrimaryStudent, Student);
var ps = new PrimaryStudent({
    name: 'XXXX',
    grade: 100
});