Returns true if this map contains the given key
.
Returns true if any of the keys in the map are equal to key
according to the equality used by the map.
bool containsKey(Object key);
© 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
https://api.dartlang.org/stable/2.0.0/dart-core/Map/containsKey.html