function a() {
var i = 0;
function b() {
console.log(i);
}
return b;
}
var c = a();
c(); 

var User = function (opts) {
var scope = this;
for (var k in opts) {
scope['get' + k] = function () {
return opts[k];
};
scope['set' + k] = function (v) {
return opts[k] = v;
};
}
};
var u = new User({
name: '测试',
age: 11
}); 

var User = function (opts) {
var scope = this;
for (var k in opts) {
(function (k) {
scope['get' + k] = function () {
return opts[k];
};
scope['set' + k] = function (v) {
return opts[k] = v;
};
})(k);
}
};
var u = new User({
name: '测试',
age: 11
}); 

function getUUID() {
var id = 0;
return function () {
return ++id;
}
}
var uuid = getUUID(); 

Util.tryUrl = function (url) {
var iframe = document.createElement('iframe');
iframe.height = 1;
iframe.width = 1;
iframe.frameBorder = 0;
iframe.style.position = 'absolute';
iframe.style.left = '-9999px';
iframe.style.top = '-9999px';
document.body.appendChild(iframe);
Util.tryUrl = function (url) {
iframe.src = url;
};
U.tryUrl(url);
}; 

var getUUID = function () {
var i = 0;
getUUID = function () {
return i++;
};
return getUUID();
}; 

<input id="input" value="input" type="button" />
<div id="div">
我是div</div>
<span id="span">我是span</span>
<div id="wrapper">
<input id="inner" value="我是inner" type="button"/>
</div> 

$.on('click', 'selector', fn) 

function delegate(selector, type, fn) {
document.addEventListener(type, fn, false);
}
delegate('#input', 'click', function () {
console.log('ttt');
}); 

var arr = [];
var slice = arr.slice;
var extend = function (src, obj) {
var o = {};
for (var k in src) {
o[k] = src[k];
}
for (var k in obj) {
o[k] = obj[k];
}
return o;
};
function delegate(selector, type, fn) {
var callback = fn;
var handler = function (e) {
//选择器找到的元素
var selectorEl = document.querySelector(selector);
//当前点击元素
var el = e.target;
//确定选择器找到的元素是否包含当前点击元素，如果包含就应该触发事件
/*************
注意，此处只是简单实现，实际应用会有许多判断
*************/
if (selectorEl.contains(el)) {
var evt = extend(e, { currentTarget: selectorEl });
evt = [evt].concat(slice.call(arguments, 1));
callback.apply(selectorEl, evt);
var s = '';
}
var s = '';
};
document.addEventListener(type, handler, false);
} 

delegate('#input', 'click', function () {
console.log('input');
});
delegate('#div', 'click', function () {
console.log('div');
});
delegate('#wrapper', 'click', function () {
console.log('wrapper');
});
delegate('#span', 'click', function () {
console.log('span');
});
delegate('#inner', 'click', function () {
console.log('inner');
}); 

e.stopImmediatePropagation()