How can i iterate through this shortcode array?

It seems like you are setting up the common Chart Options in a JS file but as all the charts are going to have different footer caption you shouldn’t set it as a common option.

As you specified that the post has three charts that means the captionLabel JavaScript variable is getting declared and being assigned the value 3 times if that is part of shortcode. So the final value assigned to the captionLabel will be label 3 and then the chart options are being set in the js file. Thus, all your charts are having label 3 as footer caption.

May be you can set the label in Chart Options on per chart basis.