Which dependence two arrays? If second array had create from the first array : I'm crate two Array, one it has the entries, second empty. 
Assing a one cell, the first array[0] to the second array.  And had applye method pop() for second Array.  Why cell,  the first array too change his a value.


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    var t = [[1,1,1], [1,1,1,1,1], [1,1,1,1]];
    var t1 = t[0];
    t1.pop();
    console.log(t[0]);

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result  1.1
Why it's happening?
Thanks.