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I've create an array in Javascript designed to hold basic details about a set of upgrades as part of a game I'm making. The upgrades are defined as follows;

var Upgrade = {Name:NameIn,
               Description:DescriptionIn,
               Image:ImageIn,
               Purchased:0,
               Visible:false,
               ID:IDIn}

I've got a standard for loop that is trying to access these variables. Yet for some reason the Description variable comes up with an "undefined" error when I try to access it using the i variable I've created as part of the loop. i.e. Upgrades[i].Description comes up as undefined.

I've checked and all of the other elements such as Name, Image etc can be accessed using the "i" variable. e.g. Upgrades[i].Name

Yet if I manually type in what i is equal to as part of my code at the time I try to access Description (e.g having Upgrades[1] as oppose to Upgrades[i]) it allows access to it.

The array is filled as such;

function AddUpgrade(NameIn,DescriptionIn,ImageIn,IDIn){
var Upgrade = {Name:NameIn,
               Description:DescriptionIn,
               Image:ImageIn,
               Purchased:0,
               Visible:false,
               ID:IDIn}
Upgrades.push(Upgrade);

AddUpgrade("Sharpened Rocks","Description",
        "img/upgrades/Caveman2.png","Caveman2Display");

Below is the loop that is trying to access the variables to send to an HTML document;

for (i = 1; i < Upgrades.length ; i++){
    if (Upgrades[i].Visible == 1){
        document.getElementById("upgrades").innerHTML += "<div class=\"upgrade\" id=\"" + Upgrades[i].ID + 
        "\" onclick=\"ButtonBuyUpgrade(" + i + ")\"><img src=\"" + Upgrades[i].Image + "\"><div class=\"hovertext\" id=\"" 
        + Upgrades[i].ID + "Hover\">" + DisplayUpgradeCost(i) + Upgrades[i].Description + "</div></div>";
    }
}

Here is the output from console;

Uncaught TypeError: Cannot read property 'Description' of undefined inc.js:161 DisplayUpgrade inc.js:161 CalculateUnlocks inc.js:463 (anonymous function) inc.js:502 Object {Name: "Sharpened Rocks", Description: "Description", Image: "img/upgrades/Caveman2.png", Purchased: 0, Visible: 1…} Description: "Description" ID: "Caveman2Display" Image: "img/upgrades/Caveman2.png" Name: "Sharpened Rocks" Purchased: 0 Visible: 1

And here is the console.dir output;

1: Object Description: "Description" ID: "Caveman2Display" Image: "img/upgrades/Caveman2.png" Name: "Sharpened Rocks" Purchased: 0 Visible: 1

All the other elements are also filled in, there are no missing pieces of information.

I'm completely confused by this and have no idea why it's happening. Any thoughts?

share|improve this question
    
There are 2 for loops: for(;;) and for( in ). Which are you using. The object you posted here might well end up having a member called Description with the value undefined. It all depends on what the value of DescriptionIn was when the object was created... –  Elias Van Ootegem Aug 20 '14 at 12:00
    
Try console.log(Upgrades) or console.log(Upgrades[i]) in your loop. –  parchment Aug 20 '14 at 12:00
    
Can we see how you fill your array? –  mrgnou Aug 20 '14 at 12:02
    
The error means that you are trying to access an element at an index that doesn't exist. console.dir your array before the loop and see if there are any holes. –  Felix Kling Aug 20 '14 at 14:49

2 Answers 2

up vote 1 down vote

Looks like you've created an object. An object is a collection of key:value pairs. An array is a collection of elements ordered by index (starting at 0), denoted by []. To loop through your object try forIn loop:

var Upgrade = {
  Name:'NameIn',
  Description:'DescriptionIn',
  Image:'ImageIn',
  Purchased:0,
  Visible:'false',
  ID:'IDIn'
}

for(var i in Upgrade) {
  console.log(Upgrade[i])
}
share|improve this answer
    
I need to access specific variables at certain points. It is effectively an array of objects, and I need to access the variables out of sequence of the object variable order. –  Mitch Douglas Aug 20 '14 at 14:36
up vote 0 down vote accepted

To close this one, it turns out the issue was due to the scope of the i variable in my loop coming from another loop the function was being called by, so the program was getting confused. I solved the issue by having the loop say (var i = 0 to create a local variable called i to use.

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