kotlin-stdlib / kotlin.collections / MutableList / add add Common JVM JS Native 1.0 abstract fun add(element: E): Boolean(source) Adds the specified element to the end of this list. Return true because the list is always modified as the result of this operation. Common JVM JS Native 1.0 abstract fun add(index: Int, element: E)(source) Inserts an element into the list at the specified index.