After using push in JavaScript, why the initial element of an array is undefined?

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The initial element of an array is undefined after using push in JavaScript because push() method adds new elements to the end of an array, thus extending the length of the array by pushing the new element to the end. When you create a new array with push() function, the array starts with an empty set of elements with a length of 0. The first element is then added to the array, but any previous elements of the array remain undefined.