Use variable contents in object?

[Bitslong]

Hi,
I'm trying to use what is held in a variable to get to an object property:

img_lib.section s is an array containing a varying number of strings - eg "Category1","Ca tegory2" etc

img_lib.Categor y1 is an array that contains a varying number of strings

In the second for statement I need to compare j to the length of the img_lib.* array as retrieved from img_lib.section s[i]

I started with the code as shown below but I don't believe it works.

Suggestions?

for (i=0; i<img_lib.sections.length; i++){
       alert("Primary Loop");
	category=img_lib.sections[i];
	cat_arr_str="img_lib.".category."[i]";
	for(j=0; j<cat_arr_str.length; j++){
		alert("Secondary Loop");
	}
				
}

[Bitslong]

Solved it by making the second for statement:

for(j=0; j<img_lib[img_lib.sections[i]].length; j++){
 alert("Do stuff");
}