例1：
var element = document.getElementById('button');
element.addEventListener("click", (function() {
// init the count to 0
var count = 0;
return function(e) { // <- This function becomes the click handler
count++; // and will retain access to the above `count`
if (count === 3) {
// Do something every third time
console.log("Third time's the charm!");
//Reset counter
count = 0;
}
};
})());
<button id="button">Click Me!</button>
例2：
var func = (function() { var a = 'val'; return function() { alert(a); }; })();
