How do I play a sound when an element changes, like SO Chat does?

问题

I want a sound to play when an element changes on a page. I know how to do this, but I can't get it to play only on the first change, and don't do it later, until the user focuses the window (tab) and blurs it again.

My current code:

var notif = new Audio('http://cycle1500.com/sounds/infbego.wav');
if (window.innerHeight === window.outerHeight) {
  $(window).bind('DOMNodeInserted', function() {
      notif.play();
  });
}

回答1:

Use a variable to represent whether the sound should be played or not.

var shouldPlayAlertSound = true,
    notif = new Audio('http://cycle1500.com/sounds/infbego.wav');
if (window.innerHeight === window.outerHeight) {
  $(window).bind({
    'DOMNodeInserted': function() {
      if (shouldPlayAlertSound) {
        notif.play();
      }
      shouldPlayAlertSound = false;
    }, blur: function() {
      shouldPlayAlertSound = true;
    } 
  });
}

Edit: I've tested this working on Firefox, Safari, and Opera (except for the innerHeight check). (Chrome doesn't support playing WAV audio files, only the MP3, AAC, or Ogg Vorbis formats.)

回答2:

If this is your only DOMNodeInserted handler, I'd just remove it when the work is done (making all future insertions cheaper), like this:

notif = new Audio('http://cycle1500.com/sounds/infbego.wav');
if (window.innerHeight === window.outerHeight) {
  $(window).bind({
    'DOMNodeInserted': function() { 
      notif.play(); 
      $(window).unbind('DOMNodeInserted'); 
    }
  });
}

If it's not the only handler that's workable too, just make it a named function:

notif = new Audio('http://cycle1500.com/sounds/infbego.wav');
if (window.innerHeight === window.outerHeight) {
  function play() { notif.play(); $(window).unbind('DOMNodeInserted', play); }
  $(window).bind({
    'DOMNodeInserted': play
  });
}

来源：https://stackoverflow.com/questions/4266852/how-do-i-play-a-sound-when-an-element-changes-like-so-chat-does