Multidimensional Array Object allocation

Question

So far, I'm trying to create a 2-Dimensional JSON array to hold a series of shapes inside a series of 'frames'. So far I thought I had it, but I can only push shapes to frame[0]; as soon as I pass it frame[1] I get the error Uncaught TypeError: Cannot read property 'shape' of undefined.

Why can't my browser recognise frame[1] as a potential next storage area for the frame array? Is it something to do with how I've initialised the JSON Array?

Relevant code so far:

function Obj(type, x, y, w, h, r) {
"use strict";
this.type = type || null; //rect, crcl, line, text
this.x = x || null;
this.y = y || null;
this.w = w || null; //used for rect, line
this.h = h || null; //used for rect, line
this.r = r || null; //used only for crcl
}
var keyframes = {
    'frame': [{
        'shape': []
    }]
};

var shape1 = new Obj('rect', 20, 20, 20, 20, 0);
var shape2 = new Obj('crcl', 20, 20, 0, 0, 20);

keyframes.frame[0].shape.push(shape1);
keyframes.frame[1].shape.push(shape2);

Pointy · Accepted Answer · 2015-05-02 16:00:53Z

3

It does recognize frame[1] as a potential place to put something, but you haven't put anything there. Your code expects frame[1] to be a reference to an object but you only initialize the first element that way.

keyframes.frame[1] = { shape: [] };

will initialize the next element. Without that initialization, keyframes.frame[1] is undefined.

answered May 2, 2015 at 16:00

Pointy

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1 Comment

Tom Sykes Over a year ago

Perfect, now I just need to remember to initialise the next frame each time one is created. Thanks!

Cyprien · Accepted Answer · 2015-05-02 16:16:01Z

1

PROBLEM:

Your initialization of keyframes is as follows:

an object
contains a 1 element array 'frame'
'frame' contains an object

You CANNOT access keyframes.frame[1] because it does not exist (frame is a 1 element array so ONLY keyframes.frame[0] is valid)

SOLUTION:

Create the keyframes.frame[1] element
- keyframes.frame.push({shape: []}); //now keyframes.frame[1] exists
push shape 2 to the object added above as you attempted before
- keyframes.frame[1].shape.push(shape2); //this should now be valid

answered May 2, 2015 at 16:16

Cyprien

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