Build the library in learn classes

these is classes course of building library link of course

i have got reference Error

ReferenceError: isCheckedOut is not defined
at new Book (/home/ccuser/workspace/learn-javascript-classes-build-a-library/app.js:45:11)
at Object.

my code link
please Help to solve these issue i am unable to find error
Thanks :smile:

super() is used to call parent method. Why would need to call the constructor multiple times? Also, looking at the parent constructor method, there is only one parameter. So calling the parent constructor should only be done once with the right argument.

thanks i understand now my error thanks for your help :smile: