Unable to get a ‘length’ property from an HTML element (array) using .hasAttribute / .hasOwnProperty methods

I have problem of getting a ‘length’ property of an array (in this case a table row), which clearly says that it has the property of length after applying the method getAttributeNames().

All the methods I try to apply (.hasOwnProperty, .hasAttribute. array.length) just return the boolean or undefined.

Might be a stupid question, but I am a newbie, and it kind of bothered me so much so I had to ask.
I hope I have explained my issue clearly.

I attach a page just in case.
https://rahulshettyacademy.com/angularAppdemo/library

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