Above output show, the notation "*2" to represent two consecutive "undefined" values, indicating their occurrence in succession. However, in cases where a single undefined value exists, the "x 1" notation could be omitted. This demonstrates that the Chrome browser employs a distinct approach to displaying uninitialized indexes within arrays.
A sparse array is characterized by non-contiguous indexes that may not begin at 0. Typically, the length property of an array indicates the count of elements it holds. In the case of a sparse array, the length property exceeds the actual element count due to gaps in index sequence. As the array becomes more extensively sparse—featuring numerous missing indexes—it loses its optimized efficiency in index-based access. In terms of performance, a sufficiently sparse array essentially resembles a hashtable, with associated access characteristics.