Using Arrays in a JavaScript class

Question

I have a JavaScript class defined as shown here:

function Item() { 
  this.init(); 
} 

Item.prototype = { 
  id: null, 
  name: '', 
  description: '', 
  init: function () { 
    this.id = "1"; 
  } 
};

I want to add a property called "logs". I want this property to be an array of other class entities. How do I define this kind of array as a property on my Item class? How do I add entities to that array? Originally, I thought I could add "this.logs = {};" in my init function. Then in my code elsewhere, I tried the following:

Item i = new Item();
i.logs.push(NewLog());

However, the push function through an error that says: "Cannot call method 'push' of undefined"

What am I doing wrong?

Rob W · Accepted Answer · 2012-02-23 13:02:00Z

2

logs is not initialized yet. Add it in the constructor (not to the prototype, because the array would then be shared by all instances of Item):

function Item() { 
  this.init();
  this.logs = []; // Not {}:   [] is equivalent to new Array(), and
}                 //           {} is equivalent to new Object() (not an array)

Also, JavaScript != Java.

var i = new Item() // instead of Item i = new Item();

answered Feb 23, 2012 at 13:02

Rob W

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2 Comments

JQuery Mobile Over a year ago

How do I add items to the array then? Once "i" is created, how do I "push" items onto the array?

Rob W Over a year ago

@JQueryMobile You said that you wanted to add elements to the logs array (which is a property of the "class instance"). Use i.logs.push(NewLog());.

blockhead · Accepted Answer · 2012-02-23 13:04:00Z

0

You can try:

Item.prototype = { 
  id: null, 
  name: '', 
  description: '', 
  init: function () { 
    this.id = "1"; 
  },
  push: Array.prototype.push 
};

answered Feb 23, 2012 at 13:04

blockhead

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