javascript - 'attacheventlistener' and 'onclick' prototype

Question

Maybe there are serval sub-questions for my problem:

• Is there a general solution to get events binded to an element?(Without jquery or others javascript librarys).
• I found $(element).data('events') can't get event registered with <element onclick="some_functions()">. How can we get it?

My goal is to insert an event before native event (registered by the programmer of html page). I found two solutions.

• Using jQuery as described here
• modify HTMLElement.prototype.addeventlister as described here

However, I find both these methods can't solve the situation like that

<element onclick="some_functions()">

Answer 1

onclick您可以通过该属性访问（和覆盖）该事件处理程序。如果你有一个

<span id="elem" onclick="some_functions()">

然后document.getElementById("elem").onclick将产生匿名函数

function (event) {
    some_functions()
}

要拦截它，您可以使用类似

var fn = elem.onclick;
elem.onclick = function() {
    console.log("before");
    var res = fn.apply(this, arguments);
    console.log("after");
    return res;
};

免责声明：这可能不会在较旧的浏览器中，我不知道内联属性事件处理程序和传统事件注册的发明者（Netscape，IE）如何处理这些。他们还不如做过类似的事情eval(elem.getAttribute("onclick"))，在任何情况下，您都可以像这样访问处理程序代码（作为字符串）。