gistfile1.js

#target illustrator

//start library
// function MyLayer() { } and function SubLayer() are constructor functions

function MyLayer(input) {
    this.doc = app.activeDocument;
    this.myLayerIndex = input || 0; 
    this.myLayerItem = this.hasLayerIndex() ? this.doc.layers[this.myLayerIndex] : false;
    this.subLayers = this.myLayerItem.pageItems;
    this.width = this.myLayerItem.width;
    this.height = this.myLayerItem.height;
};

MyLayer.prototype.hasLayerIndex = function() {
    return this.myLayerIndex <= this.doc.layers.length - 1;
};



function SubLayer(pageItem) { 
    this.subLayers = [];
    this.pageItem = pageItem; 
    this.myLayerItem.pageItems.each(function(pageItem) {
        this.subLayers.push(new MyPageItem(pageItem));
    });
} 

SubLayer.prototype.isIn = function() {
    parentVB = parentItem.visibleBounds;
    return this.left >= parentVB[0] && 
           this.top >= parentVB[1] && 
           this.right <= parentVB[2] && 
           this.bottom >= parentVB[3];
};

//start script

var parentLayer = new MyLayer(0);
var parentSubLayers = parentLayer.subLayers;

var currentLayer = parentSubLayers[1];
var checkLayer = subLayersTwo.subLayers[0];

currentLayer.isIn(checkLayer);