Status of a javascript var after trying to retrieve an unexisting array entry?

Status of a javascript var after trying to retrieve an unexisting array
entry?

References

Reference NO 1

http://stackoverflow.com/questions/15185628/status-of-a-javascript-var-after-trying-to-retrieve-an-unexisting-array-entry

Reference NO 2

http://stackoverflow.com/questions/8749263/delete-operator-behavior-on-non-existing-indexed-element-of-an-array

Reference NO 3

https://github.com/sole/tween.js/

Reference NO 4

http://www.tutorialspoint.com/javascript/javascript_error_handling.htm

Reference NO 5

http://vgaltes.com/index.php/2013/03/16/testing-with-casperjs-part-2/

Reference NO 6

http://docs.moodle.org/dev/lib/formslib.php_Form_Definition

Reference NO 7

http://www.yiiframework.com/wiki/152/cookie-management-in-yii/

Reference NO 8

http://en.wikibooks.org/wiki/Tcl_Programming/Functions