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/Dart 2

dart:html

containsKey method

bool containsKey (Object key)

Implementation 

bool containsKey(Object key) => _getItem(key) != null;

© 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
https://api.dartlang.org/stable/2.0.0/dart-html/Storage/containsKey.html