I don't understand array in Javascript 😞😞

Question

Can you help me expland this program. I think it so easy with someone but I can figure out how it work and go to output the result 0,1. Why it not 1,3???
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var arr=[];
arr[0]=arr.length;
arr[1]=arr.length + arr[0];
document.write(arr);

Answer 1

in the first statement arr.length =0 because there is not any element in the array so arr[0]=0 and in second statement arr[1]=1 because after first statement
arr contain one element 0 so array length is 1 hence it shows 0,1 hope this is helpful for you

Answer 2

Because the array has a size of 0 until you add elements

Answer 3

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