About js objects

Question

my English is not so good, but i try to explain my self clear. I just started learn JS objects and stumbled upon the problem that i can't understand.

I got a simple object like

var cars = {
   doors: 4,
   wheels: 4
}

and when i trying to create an object like this:

   var Opel = new car()

I got an error Uncaught TypeError: object is not a function

And when i do it like this :

Opel = Object.create(cars)

all going fine.

And when i writing a an Object like this :

 function cars() {}

a method to declare the object with new, work correctly. I can't understand what the difference between thous two type of writing the objects.

Thanks for advice.

Please keep reading the tutorials on JS, it will come to you. Meanwhile, SO is not really designed to be a replacement for learning a language on your own. — , Aug 23 '14 at 19:24
I recommend to read the MDN JavaScript Guide: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Working_with_Objects , which explains all the different ways of creating an object. — Felix Kling, Aug 23 '14 at 19:25
I'm understand, that when i write it like a function it is constructor.it is different from PHP, but why without it gives an error when i declaring it with new? because it's don't have constructor? — Victorino, Aug 23 '14 at 19:26
Maybe the following answer can help. It answers what a constructor function does and what prototype does: http://stackoverflow.com/a/16063711/1641941 — HMR, Aug 23 '14 at 19:26
You can only call **functions** with `new`. As the error tells you, `car` is not a function, hence you can't call it with `new`. — Felix Kling, Aug 23 '14 at 19:31

score 1 · Accepted Answer · answered Aug 23 '14 at 19:24

1

You didn't understand prototyping correct.

To define a class you create a simple function, like:

function Car(){
   this.doors = 4; //For instance, not really necessary 
}

You can set properties on this in the function.

Then you define a prototype, every object of class "Car" will have all this properties (and "methods"):

Car.prototype = {
   doors: 4, //we don't need to set this again if we already did in the constructor, but I'll leave if it anyway
   wheels: 4
}

answered Aug 23 '14 at 19:24

idmean

thanks. one more question. when i creating a object like var foo = {} what this means? i came from PHP and in js it is different as i see – Victorino Aug 23 '14 at 19:28
1

@Viktorino You create an empty object, like `new stdClass()` in PHP or an empty associative array. In JavaScript there are no instances of a class, only objects which were created from a prototype and therefore have the object's functions (methods) and properties (instance variables) – idmean Aug 23 '14 at 19:30
1

@Viktorino `foo={doors:4}` is an instance of an object (object literal) Not sure what the equivalent in PHP is but I think it would be an array `array('doors'=>4)` If you need to create many instances with roughly the same characteristics you use a constructor function in JavaScript or a class in PHP. – HMR Aug 23 '14 at 19:31
aaaa.. now i understand it. thank you for help! – Victorino Aug 23 '14 at 19:32

1 Answers1