How do method cascades work exactly in dart?

As pointed in the official Dart language article Method Cascades in Dart:

The “..” syntax invokes a method (or setter or getter) but discards
the result, and returns the original receiver instead.

In brief, method cascades provide a syntactic sugar for situations
where the receiver of a method invocation might otherwise have to be
repeated.

Below are example based/copied from the previously cited article. For further information, go read it.

add() example

In the scenario where one want to add multiple elements to a list, the legacy-way is to do multiple assignements :

myList.add("item1");
myList.add("item2");
// add again and again…
myList.add("itemN");

While you can’t do something like myList.add("item1").add("item1")….add("itemN"); as the add() does not method return the myList object but a void, you can use the cascading operator instead as it discards the result, and returns the original receiver myList :

myList..add("item1")..add("item2")…..add("itemN");

myList.add("item1").add("item2")….add("itemN");

Another example

So Instead of writing:

var address = getAddress();
address.setStreet(“Elm”, “13a”);
address.city = “Carthage”;
address.state = “Eurasia”
address.zip(66666, extended: 6666);

One may write

getAddress()
 ..setStreet(“Elm”, “13a”)
 ..city = “Carthage”
 ..state = “Eurasia”
 ..zip(66666, extended: 6666);