A callback is a function that is passed as an argument to another function and is executed after its parent function has completed<html><head>
<title>callback function</title>
<script language="javascript" type="text/javascript">
function fParent(callback) {
alert("This is parent function");
alert("Now call the callback function");
callback();
}
function fCallback1() {
alert("This is callback function 1");
}
function fCallback2() {
alert("This is callback function 2");
}
function test() {
fParent(fCallback1);
fParent(fCallback2);
}
</script>
</head>
<body>
<button onClick=test()>click me</button>
</body>
</html>
原文：http://www.cnblogs.com/erictanghu/p/3595781.html