Why does my 'mailto' function not work after an if statement

I am writing a function that has to check 8 inputfields of a form. If all of them are filled in by the user, the 'mailto' function should open the email client. The function until now does all the stuff that is necessary, except for opening the email client. The if/else statements themselves work fine, as the alert boxes I put after those statements correspond correctly. The 'mailto' function works fine when I put it outside the if/else statements, but then it will open despite the fact that not all inputfields are filled in. Why does the email client not open after the if-statement, even though the alert box after the very same if-statement does show.