Confuse terms in Angular JS tutorial - angularjs

Question

I'm following a tutorial and I have difficulties to understand a certain sentence which talks about the problem that can occur when naming my properties in Angular:
It quietly tolerates all property access errors, including nested properties on nonexistent parents and out-of-bounds array access.
aliasing variables as a way to cope with variable shadowing
My english is good enough to know what is written, but I really don't understand what is "nested properties on nonexistent parents" and "aliasing variables as a way to cope with variable shadowing". I did some research, but couldn't clearly understand.
Could someone give me a clear explanation?

Answer 1

Suppose you have:
obj : {
first: {
second: [1, 2, 3]
}
}
Trying to do this:
obj.nonexistent.prop // Nested property on nonexistent parent
obj.first.second[1000] // Out of bound array access
Would throw an error in javascript, but Angular doesn't throw an error
For aliasing variables as a way to cope with variable shadowing, imagine this:
<div ng-controller="ItemsController">
<div ng-repeat="item in items" ng-init="outerCount = $index">
{{outerCount + 1}}. {{item.name}}
<div ng-repeat="item in item.items">
{{outerCount + 1}}.{{$index + 1}}. {{item.name}}
</div>
</div>
</div>
From here
In an ng-repeat, the $index variable changes to point at the current index of the loop each iteration. So if you have nested loops, you'll lose a reference to the outer $index variable. This is variable shadowing. To use the outer variable, you can use ng-init and set it to the $index outside. Now, you've aliased the outer $index variable to outerCount.
Hope this is clear!