My question is if I use an array like this,

var arr1 = [1, 2, 3, 4];
console.log(arr1.length); // 4 (Expected)

If I update the length property, the array gets updated too.

arr1.length = 0;
console.log(arr1); // []

I'd like to know how this is being done (the internals)?

Also, I'm not sure if getter and setter methods of the property length (that are ways to run a function if the property gets accessed or set) are used here. I think they're not.

If it's being used, length should not be visible directly when I expand the array in the browser console. But we get the length directly without running any functions.

The console when I use get/set for a property of an object,

Getting the value of length property directly without running any functions,