In JavaScript, arrays and objects serve different purposes and have different performance characteristics based on how they are used.
Arrays are ordered collections of data, typically indexed by integers starting from 0. They are optimized for random access by index, making them efficient for operations like iterating through elements, accessing elements by index, pushing and popping elements at the end, and using array methods like forEach(), map(), filter(), etc.
Objects, on the other hand, are collections of key-value pairs where keys are strings (or Symbols) and values can be any data type. They are optimized for fast lookup by key. Objects are useful for storing and accessing data by named properties. They are efficient for operations like adding, updating, and deleting properties by key.