array[key] returns undefined, even though array[0] is defined, and key defined

In my nav item directive (the last one):

pantherDirectives.directive('bootstrapNavBar', function() {
    return {
        scope: {},
        templateUrl: 'partials/directives/bootstrapNavBar/wrapper.html',
        transclude: true,
        replace: true
    }
}).directive('navBarHeader', function() {
    return {
        scope: {},
        templateUrl: 'partials/directives/bootstrapNavBar/header.html',
        transclude: true,
        replace: true
    }   
}).directive('navBarBody', function() {
    return {
        scope: {},
        templateUrl: 'partials/directives/bootstrapNavBar/body.html',
        transclude: true,
        replace: true,
        controller: function($scope, $element) {
            this.items = [];
        }
    }   
}).directive('navBarDropDown', function() {
    return {
        scope: {},
        transclude: true,
        replace: true
    }   
}).directive('navItem', function() {
    return {
        scope: {},
        transclude: true,
        require: '^navBarBody',
        template: '<li ngclass="" ng-click="" ng-class="thisItem"><a data-ng-transclude></a></li>',
        replace: true,
        priority: 1000,
        controller: function($scope, $element, $attrs) {

        },
        link: function(scope, element, attrs, navBarBody) {
            var itemNum  = navBarBody.items.push(false);
            var thisItem = navBarBody.items[itemNum];

            console.log(itemNum);               //returns 1 then 2
            console.log(thisItem);             // returns undefined
            console.log(navBarBody.items[0]); //  returns false (as intended)
        }
    }
});

my key variable itemNum returns something, as does my array when I specify a number as the key, but when the key is my variable I get an undefined.

Array.push() returns the new length of the array. Thus, when you push an element into an empty array, you will be returned 1, but the element will be accessible at array[0] (0-indexed), and not array[1] which is how you are trying to access it.

var arr = [];             // length is 0
var len = arr.push(false);// returns 1 because array's new length is 1
console.log(arr[0]);      // this works because what you pushed is at index 0
console.log(arr[len]);    // won't work because you are essentially doing arr[1]
                          // i.e trying to access the second element (which doesn't exist)