Introduction to Object-Oriented JavaScript - MDC Docs

Introduction to Object-Oriented JavaScript - MDC Docs(developer.mozilla.org)

40 points by willyg 15 years ago | 14 comments

giberson 15 years ago |

Under the section "The Property (object attribute)" the code segment has two curious lines. I expect the first cancels out the latter, making the latter useless.

     // in Person function
     this.gender = gender;
     // outer scope (gender will never be this value because it is overridden by the person constructor argument)
     Person.prototype.gender = 'Person Gender';

Am I correct, or does the prototype.gender line have some other purpose than instantiating gender to a value that is immediately overridden by the passed in value (or undefined if no value is passed)?

qqqq2010 15 years ago | |

It's ensuring a default value basically. If you instantiate a person without an argument and try to reference this.gender later, you'll throw a script error. This is just avoiding that.

A way I'd prefer might look like this:

  function Person = function(gender) {
      this.gender = gender || 'neuter' //the sauce that defines a fallback
  }

giberson 15 years ago | | |

This is not the case, because in the constructor person is being set to the argument. If the argument is not supplied (undefined), calling the instantiated object's gender property will result in undefined. [tested and confirmed]

juliangutman 15 years ago | |

Presumably if the gender property is deleted the prototype.gender will come through

nprincigalli 15 years ago |

Might want to check the Joose object system (http://joose.it/ #joose on irc.freenode.net), highly inspired in the awesome thing that Moose (http://search.cpan.org/dist/Moose/) is to Perl. There's even a port of KiokuDB as KiokuJS!(http://joose.it/blog/2011/01/13/introducing-kiokujs/) :)

clemesha 15 years ago |

It's good to know this stuff, but in my real-world usage of JavaScript, I've become a big fan of Backbone.js to help structure code intelligently, etc.

voidr 15 years ago |

> Inheritance A Class can inherit characteristics from another Class.

Somebody should tell Mozilla, that there are no classes in JavaScript....

johncoltrane 15 years ago | |

The document is probably targeted at newcomers from other languages. But still…

erez 15 years ago | |

The guide says that immediately after the terminology paragraph

johncoltrane 15 years ago | | |

But comes back to it at the Custom Objects part(1). And everywhere. They don't use "class" as a keyword, though, but more in a CS way which can be problematic because other keywords like "prototype", "array" or "object" mean pretty much the same thing in both contexts.

An interesting ressource, anyway.

(1) https://developer.mozilla.org/en/Introduction_to_Object-Orie...

sjs 15 years ago | |

Please don't make us start saying "object used as a class".

voidr 15 years ago | | |

The first step to learning JavaScript is to forget about class-ical OOP, you can't write good code if you start forcing class-ical concepts on JavaScript, it's a prototypical language encouraging people to treat it as something else is wrong.

rgbrgb 15 years ago |

I really like Mozilla's docs. I read this one recently actually.

// in Person function this.gender = gender; // outer scope (gender will never be this value because it is overridden by the person constructor argument) Person.prototype.gender = 'Person Gender';