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run code in 200+ php & hhvm versions
Bugs & Features
<?php $array = json_decode('{"1":"1","2":"1","3":"1","4":"1","12":"1"}' , true); var_dump($array); var_dump(array_key_exists("12", $array));
based on pXlRu
Output for 5.6.0 - 7.1.7
array(5) { [1]=> string(1) "1" [2]=> string(1) "1" [3]=> string(1) "1" [4]=> string(1) "1" [12]=> string(1) "1" } bool(true)