You don't need to pass this, there already is the event object passed by default automatically, which contains event.target which has the object it's coming from. You can lighten your syntax:

This:

<p onclick="doSomething()">

Will work with this:

function doSomething(){
  console.log(event);
  console.log(event.target);
}

You don't need to instantiate the event object, it's already there. Try it out. And event.target will contain the entire object calling it, which you were referencing as "this" before.

Now if you dynamically trigger doSomething() from somewhere in your code, you will notice that event is undefined. This is because it wasn't triggered from an event of clicking. So if you still want to artificially trigger the event, simply use dispatchEvent:

document.getElementById('element').dispatchEvent(new CustomEvent("click", {'bubbles': true}));

Then doSomething() will see event and event.target as per usual!

No need to pass this everywhere, and you can keep your function signatures free from wiring information and simplify things.

Update 2022-10-30:

I have contacted someone from WHATWG, and another way it could be done is below, although some IDE's report it as "obsolete" which it's not. You could pass the "event" keyword (no capital E) in your caller's argument list, in any position, and use it as such.

Below would work, a, b, c and d being extra arguments to pass if any, to demonstrate the order doesn't matter:

<p onclick="doSomething(a,b,event,c,d)">

And in your function definition, you would capture it accordingly:

function doSomething(arg1, arg2, arg3, arg4, arg5){} //arg3 would contain the event

And access the usual properties, in this case since we wired event with arg3:

console.log(arg3.target)

Since inline events are executed as functions you can simply use arguments.

<p id="p" onclick="doSomething.apply(this, arguments)">

and

function doSomething(e) {
  if (!e) e = window.event;
  // 'e' is the event.
  // 'this' is the P element
}

The 'event' that is mentioned in the accepted answer is actually the name of the argument passed to the function. It has nothing to do with the global event.

Here is how I would do it to prevent users from copying and pasting invalid characters into input text fields:

function validatePaste(el, e) {
  var regex = /^[a-z .'-]+$/gi;
  var key = e.clipboardData.getData('text')
  if (!regex.test(key)) {
    e.preventDefault();
    return false;
  }
}

This function is located inside <script> tags and it is called like:

<input type="text" onpaste="validatePaste(event)">

This would answer the question perfectly without having to worry about deprecation issues.

function doSomething(e){
  // instead of e.target, use just 'e'
  console.log(e)
}

<p id="p" onclick="doSomething(this)">
   <a href="#">foo</a>
   <span>bar</span>
</p>