Whether or not you think that pop-ups are a modern form of pestilence, like locusts and Britney Spears CDs, there are times when they are a necessary evil. Many Web-based applications use pop-ups for a number of mundane tasks ranging from displaying help pages to displaying different images of available products. Unfortunately, if the client's browser has a pop-up blocker installed and enabled then you're pretty much out of luck when it comes to using pop-ups.
One possible solution is to have messages throughout your site saying something like, "This site utilizes pop-up windows. Please ensure that your pop-up blocker is disabled for this site." But that's not very user-friendly to make someone deactivate the blocker just to use your site. What's needed instead is a way to tell if a user has a pop-up block so that your site can then tailor the browsing experience.
Use a pop-up to kill a pop-up
The method that I've chosen to accomplish this task is by trying to open a pop-up window. Of course, this means that I have to be rather defensive in my programming because if I'm not, the possibility exists for the client seeing an error. With this in mind, I installed the Google Toolbar and began to code a page with an onload event handler that checks for pop-up blocking software. The results of this endeavor are shown in Listing A and Listing B.
The way that the page shown in Listing A works is that the onload event handler, setEvents, is fired and it attempts to open the page popupChild.html shown in Listing B. While it may seem that an error trap is enough to determine if the pop-up worked, that isn't always the case. Depending on the pop-up blocker installed there may or may not be an error. What's needed is essentially for the child window to stand up and say, "Hello, world!" or something along those lines. The page then uses the setTimeout method to delay the invocation of the function checkChild; this gives the pop-up the time needed to alter a hidden input object on the parent window and close itself. Once this has been accomplished, the function checkChild checks the value of the hidden input object to determine if the child window modified its contents. If the contents have changed, then the pop-up worked, which means no pop-up blocking software.
The two hardest parts of this entire testing process are accessing the hidden input object on the parent window and estimating how long it should take for the pop-up to open. The first problem is easily solved through the use of the Document Object Model's window.opener property. The second part is a lot harder; after all, as I play around with these examples the browser and the server are on the same machine. So while these examples worked for me, they might not work for everyone everywhere. There has to be a better way.
A better way
One of the reasons that I developed this code is because, recently, several developers and technical support people spent three hours in a conference room dealing with this issue on our order entry system. A remote client insisted that they didn't have a pop-up blocker; only after having exhausted all possible problems on our end did someone suggest reviewing the client's installed programs. Near the bottom of that list was a program that added cute little smiles to the client's e-mails. After a little research it was determined that not only did it add smiles to e-mail, but among other things, it also blocked pop-ups. The user had installed a pop-up blocker and didn't even realize it, which is the problem that I'm trying to avoid in the future with this code.