In JavaScript, Array.length is a built-in property that returns the number of elements in an array. It is automatically updated when elements are added or removed. For example, arr.length would return 5 if the array has five elements.
On the other hand, Array.size() is not a standard JavaScript method. Some libraries, like Map or Set, use .size to return the number of elements. However, for arrays in JavaScript, you should use .length to get the count of items. If you encounter .size() with arrays, it’s likely from a custom implementation or library.