阻止将新事件附加到元素

Question

I am binding event to an element.

How to prevent new JavaScript event to be bound to it?

I want to prevent unknown scripts to play with my elements.

Answer 1

You cannot block an unknown script from attaching an event listener to your object. The browser does not offer that feature. The browser does block scripts that are running from other domains (other windows, tab, or frames) from messing with your DOM, but if a script is in the same domain or even in the same page, it is free to do whatever it wants to the DOM in that page.

If you have problems with unknown scripts doing bad things, then you're probably better off backing way, way up and describing what you're really trying to protect against because trying to block an event listener is like trying to keep someone out of one drawer when they're already roaming free through your house. You probably need to secure things at a much higher level.

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If you want to get into the realm of "hacking" to try to block specific types of code, there are some options. These aren't foolproof if the 3rd party code wants to get around them. In other words, these would be more useful if you can see what the 3rd party code does and it won't adapt itself to try to get around you:

Firstly, you can replace elem.addEventListener() after you've installed your event handler which will prevent other code from using elem.addEventListener() on that object again.

var item = document.getElementById("test");
item.addEventListener("click", function() {
    log("original event handler");
});

// install "do nothing" override method
item.oldAddEventListener = item.addEventListener;
item.addEventListener = function() {};

// this one will do nothing because addEventListener has been replaced
item.addEventListener("click", function() {
    log("2nd event handler");
});

Demo: http://jsfiddle.net/jfriend00/C5rzN/

This isn't foolproof as there are other ways to still install an event handler calling the method directly from the prototype or using the onclick property.