Update casceding_style_sheet.md

Create collapsible_list.md

Create category_filter.md

Create infinite_scrolling.md

Create second_largest_number.md

Create sum_of_digits.md

Create flaten_object.md

Create reverse_string.md

Create balanced_parenthesis.md

Update js_quesions.md

Update js_quesions.md

Update js_quesions.md

Update js_quesions.md

Create pure_function.md

Create debouncing_throttling.md