abstract fun add(index: Int, element: E)

Inserts an element into the list at the specified index.

This method is redeclared as abstract, because it's not implemented in the base class, so it must be always overridden in the concrete mutable collection implementation.

open fun add(element: E): Boolean

Platform and version requirements: JS

Adds the specified element to the collection.

Return true if the element has been added, false if the collection does not support duplicates and the element is already contained in the collection.