Jmeter DOES NOT support Javascript.
As per Jmeter FAQ:
JMeter does not process Javascript or applets embedded in HTML pages.
. . . If the page uses Javascript to build up a URL or submit a form,
you can use the Proxy Recording facility to create the necessary
sampler. If this is not possible, then manual inspection of the code
may be needed to determine what the Javascript is doing.
JMeter is a tool for testing server code, not the client one. Both
recording and playback happens at the HTTP layer.
What you can do in your case is:
- use any traffic inspector tool to record http request (upon "Save");
- analyze request and its parameters sent;
- setup request manually in jmeter.
Check/unchecking check box in your scenario doesn't generate any traffic itself BUT sets the value of request parameter sent along with further http request upon further "Save".
You have to set value of this param manually to the value which is equivalent to "checked" state of check box.