I have been learning about inheritance in JavaScript, and could not understand a line of code in the tutorial at https://www.tutorialsteacher.com/javascript/inheritance-in-javascript .
The code is as follows:
function Person(firstName, lastName) {
this.FirstName = firstName || "unknown";
this.LastName = lastName || "unknown";
}
Person.prototype.getFullName = function () {
return this.FirstName + " " + this.LastName;
}
function Student(firstName, lastName, schoolName, grade)
{
Person.call(this, firstName, lastName);
this.SchoolName = schoolName || "unknown";
this.Grade = grade || 0;
}
//Student.prototype = Person.prototype;
Student.prototype = new Person();
Student.prototype.constructor = Student;
var std = new Student("James","Bond", "XYZ", 10);
alert(std.getFullName()); // James Bond
alert(std instanceof Student); // true
alert(std instanceof Person); // true
The part I do not understand is the line right after the commented line, which is:
Student.prototype = new Person();
To my understanding, when an object instance is created, its __proto__
property points to the class's prototype object.
Following this logic, shouldn't the code be:
Student.prototype = new Person().__proto__;
?
I would really appreciate some clarification!
There's a functional difference. Your way assigns Student's prototype as a reference to Person's. Mutations to either prototype will occur in both. In contrast, when you assign as in the example, you're passing a new Object
with a (deep) copy of Person's prototype. Have a look at the following screenshots.
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