Cannot set property 'name' of undefined JS

Question

I'm trying to understand JavaScript prototype and when I attempted coding this I get an error:

function Person(firstname, last name) {
  this.firstname = firstname;
  this.lastname = lastname;
}

var A = new Person('John', 'Doe');

A.prototype.name = 'Toby';

I get an error stating cannot set property 'name' of undefined. Can't i assign a property on it's prototype of Object A. This is just a simple exercise to get an understanding of prototypes

`first name`, `last name`, variable name cannot contain space — Tushar, Apr 01 '16 at 03:39
@Tushar thanks corrected it. Typo error. Still having the error though cannot set the property name — Jennifer Fitzgerald, Apr 01 '16 at 03:41
After you fix your syntax errors (spaces inside variable names), you should set the prototype property of the "class" (`Person`), not of the object you instantiate (`A`). — , Apr 01 '16 at 03:41
@torazaburo so basically when the Object A was created it inherits the base Object prototype right. — Jennifer Fitzgerald, Apr 01 '16 at 03:46

score 3 · Answer 1 · answered Apr 01 '16 at 03:42

3

Objects don't have a prototype property (unless you create one). You usually only assign to the prototype property of constructors:

function Person(firstname, lastname) {
  this.firstname = firstname;
  this.lastname = lastname;
}

Person.prototype.name = 'Toby';

var A = new Person('John', 'Doe');

// A.name === 'Toby';

answered Apr 01 '16 at 03:42

Paul

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Now everyone's named Toby. – Greg Herbowicz Nov 13 '17 at 20:30

Cannot set property 'name' of undefined JS

1 Answers1