calling function based on dom change

I rewrote a bit of my code based on that it's not really feasible to check to see if a javascript variable changes. But, how would I do it with a dom element? For instance

<div id='foo'>123</div>
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$('#foo').html('456');
// function gets fired since #foo changed.
</script>

I tried

$("#foo").change(function () {
      alert('change!');
    })
    .change();

but no luck.

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See:

• Detect div content changes with jquery
• Custom events in jQuery open doors to complex behaviors