 a read-only <a href="Set.html" class="tsd-kind-class">go.Set</a> that holds all of the keys of a Map.
Iterating over that Set will produce values that are the keys in the Map.</p>
<p>For compatibility with versions of GoJS before version 3.0, the following synonyms are defined:</p>
<ul>
<li><strong>getValue(key)</strong>: <a href="Map.html#get" class="tsd-kind-method">get</a>, but returns null instead of undefined when key is not present</li>
<li><strong>add(key,val)</strong>: <a href="Map.html#set" class=