js代码：
(function(){
var jQuery = window.jQuery = function( selector, context ) { return new jQuery.prototype.init( selector, context );
}; window.$ = jQuery; jQuery.fn = jQuery.prototype = {init: function( selector, context ) {var elem = document.getElementById(selector);if ( elem ) {this[0] = elem;this.length = 1;return this;} },append: function() {alert(arguments[0]);}
};
//为后面的实例化，将jQuery.prototype赋给jQuery.prototype.init.prototype，这个很重要
jQuery.prototype.init.prototype = jQuery.prototype;jQuery.extend = jQuery.fn.extend = function() { var target = arguments[0], length = arguments.length;if ( length == 1 ) { target = this; //这里很重要，this给target，才能使用$.i = 0;}if ( (options = arguments[0]) != null ) {for ( var name in options ) {if ( options[ name ] != undefined ) {target[ name ] = options[ name ];}}}return target;
}; jQuery.extend({isFunction: function( fn ) {return !!fn && typeof fn != "string" && !fn.nodeName && fn.constructor != Array && /function/i.test( fn + "" );}
});
})();html代码：
<html>
<head>
<script type="text/javascript" src="jmin.js"></script></head>
<body>
<div id="did"></div>
<script type="text/javascript">
function f(){};
$("#did").append("<div>append</div>");
alert($.isFunction(f));
</script>
</body>
</html>
