How to run a function based on the value of a checkbox

I am very new to Adobe Acrobat DC and I am just trying to run some very basic JavaScript, but I seem to be struggling. I have a checkbox called 'AP', and when it is checked, I would like the checkbox 'Pnr' to be grayed out and disabled. I have found a function that makes this possible, and when I run just the function in the "Mouse Up" call of the 'AP' checkbox, it does indeed disable and gray out 'Pnr'. My problem is that it grays it out every time I click the check box, but I only want it to gray out when the check box is checked and becomes enabled when it is not checked. I have found a bunch of different scripts to put in the "Mouse Up" of the check box, but I am having no success. I have tried an if statement, but that did not appear to work either. I am hoping someone might be able to help me.