Q:

Detecting mouse click on div with Javascript without side-effects

I want to detect whenever someone clicks in a div (essentially I want to know when a user is interacting with a section of text on my site, be that by selecting some text or clicking on a link), but I don't want to interfere with what the user is doing.
If I put a onmousedown or onclick event on the div it ends up breaking selection, links, etc. Is there any way to catch these events without causing any interference ?

A:

Onmousedown or onclick shouldn't interfere with anything as long as it doesn't return false;.
You can do this:
document.getElementById("spy-on-me").onmousedown = function () {
    console.log("User moused down");
    return true; // Not needed, as long as you don't return false
};

If you have other scripts that are attaching behaviour via this method on the page, then to prevent overriding them you can do:
var spyElement = document.getElementById("spy-on-me");
var oldMousedown = spyElement.onmousedown;
spyElement.onmousedown = function () {
    console.log("User moused down");
    if(oldMousedown) oldMousedown();
};

